♪♪ ♪♪ ♪♪ ♪♪ -Today on "America's Test Kitchen," Bridget and Julia uncover the secrets to the ultimate millionaire's shortbread, Adam reveals his top pick for serrated knives, and Elle makes Bridget an elegant French favorite -- gâteau Breton.

It's all coming up right here on "America's Test Kitchen."

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♪♪ -Today, we're making a well-loved British cookie called millionaire's shortbread.

It's a sturdy shortbread topped with caramel and chocolate.

It's kind of like the original Twix bar.

-We don't have to choose the right or left one, though.

-I know.

-We get to eat it all.

-Whole pan.

-It's a triple-level threat in terms of cookies.

You've got that shortbread bottom.

You've got kind of this toffee-caramel filling and then chocolate right on top.

-Mmm.

-So it's millionaire's because it's rich, lots of rich ingredients, and, also, you know, it's a little bit more expensive to make than the original shortbread, so that has something to do with the name.

So this is 2 1/2 cups of all-purpose flour.

Going to add 1/2 cup of granulated sugar and 3/4 teaspoon of salt.

Now, you'll see salt going into just about every part of this recipe because millionaire's shortbread can also be a little too sweet.

So I'll whisk this together.

All right.

So that looks good.

So now, we're going to add melted butter.

So this is 16 tablespoons of unsalted butter.

We're just going to pour this over our dry ingredients and then work it in.

You're going to see it's going to turn really, really thick, and since we're using melted butter and not creaming butter or cutting in cold butter, this is going to be a lot more sturdy.

We want to make sure that we get any of those flour pockets on the bottom of the bowl worked in, too.

It's kind of a dough at this point.

So you can see how thick that is.

-Yeah.

-So let's bring it over to our pan.

Now, this is a 9x13-inch pan.

Gone ahead and lined it with a foil sling.

Very important any time you're making any kind of bar cookie, which this is, and it's two pieces of foil, and we've shaped it so that one goes right across, and the other one goes right in.

This is going to make it easy to just retrieve it out of the pan and slice it.

So I'll crumble this over just to distribute it a little bit more evenly at the start.

You can smell that butter.

-Mmm.

-Oh, it's a good day.

So now I'm going to use my hand and just press this out into an even layer so that our next layer, which is the caramel, will also be nice and even.

This is looking pretty good, and it's going to continue to even out as it bakes in the oven.

All right.

So now, before we put it in the oven, we take a fork, and we're just going to make little marks about an inch apart from each other.

-If you didn't do this, the shortbread would sort of bubble up in places, and you'd have these big, ugly lumps, not a nice, even shortbread.

-Unh-unh.

All right.

So this is going to go into a 350-degree oven, and it'll stay in there until the top gets nice and light brown.

It's going to take about 25, up to 30 minutes.

We'll also notice that the top will feel nice and firm.

Oh, it smells so good.

Look at that beautiful shortbread.

-Beautifully even and golden.

-So I'm just going to take my hands gingerly.

It's hot, but I just want to make sure that that surface is nice and firm.

Now, we do want to compact this a little bit, because later on when we go to slice it, we don't want it to crumble all over the place.

We know we're going to get some crumbling.

We don't want too much.

So we're going to use just a burger flipper, as I like to call it, a big, long metal spatula, and press down in there.

Now, the spatula can get a little bit hot, so you might want to grab the top of it with a towel.

By the time you get to the second side, it gets really hot.

And this is great because it's also going to compact right into those corners.

All right.

So we're going to let this sit here.

You want to let it cool down for at least 20 minutes before you top it, but you can actually let it cool completely, as well.

Gives us time to talk a little bit about the caramel.

-Ooh, the good part.

-Yes, and this is almost -- I like to call it a caramel-toffee mixture because it is much deeper in flavor than a traditional caramel.

And, actually, we found that the recipes all start with sweetened condensed milk.

This is one 14-ounce can.

-So sweetened condensed milk because caramel can be very chewy and sticky, and this makes it a little softer, so easier to eat.

-Exactly.

-Mmm.

-I give that to you.

[ Both laugh ] And we have 7 ounces, or 1 cup, of firmly-packed brown sugar.

You can use light.

You can use dark.

We also have 1/2 cup of corn syrup, and that's really going to help the caramel stay nice and chewy.

Stick of unsalted butter -- 8 tablespoons just cut into small pieces.

And 1/2 teaspoon of salt.

Now, we did find, when we were cooking this, that sometimes the butter would start to split and you'd end up with kind of a greasy layer on top of the caramel, and it all had to do with how much they cooked the sweetened condensed milk.

So what we found is the more that they cook it, the more the whey proteins in the milk were broken down, and they're needed in there to keep the butter together.

So we're adding 1/2 cup of heavy cream, which has just the right amount of whey proteins, and our butter will not split.

-So heavy cream makes a foolproof caramel layer.

-Exactly.

So we're going to put this over medium heat.

I'll stir it every once in a while.

It's not like a traditional caramel that you don't want to stir.

We want to cook this until it reaches between 236 to 239 degrees.

That's going to give us exactly the right texture of caramel.

That's going to take anywhere between 16, maybe up to 20 minutes.

-All right.

-We have achieved the right temperature, anywhere between 236 and 239.

Perfect.

-It smells amazing.

[ Inhales ] Ah, it smells like toffee and a little coffee.

Ooh, that's going to taste good.

-Mmm!

It's going to taste great.

All right.

We want to get this out of the pan.

Going to pour it right onto our crust.

-That looks so pretty, having you pour it right on like that.

-We're just going to smooth this over into the corners.

You can use an offset spatula if you like.

And I just want to finish smoothing it out.

So good.

All right.

We do want to let this completely cool.

That's going to take at least 1 1/2 hours, and then we can move on to the chocolate top.

The caramel is set.

-It's beautiful.

-It's completely cool, and it's nice and firm.

It is gorgeous, isn't it?

-Yeah.

It's got a nice mirror finish.

-Well, we're going to cover it all up with chocolate.

-It's all good.

-So we're starting off with 6 ounces of bittersweet chocolate, and we've chopped this very fine.

That's very important for our tempering method because we want this to melt evenly.

So we're going to microwave this at 50% power.

And I'll stir it every 15 seconds, until it's just melted.

We don't want to overheat the chocolate at this point.

We're going to pull it out when the bottom of the bowl is just slightly warmer than my hand.

All right.

So this is looking good.

It's just a few pieces of chocolate that are still unmelted in there, but as I stir this, I know that they're going to melt right in.

So this total melting process up to this point it's only going to take one to two minutes, depending on the microwave.

So this looks good, and now, we're going to add more chocolate.

This is 2 ounces of bittersweet chocolate very finely grated.

-Yeah.

-So we're going to pour this in here.

We're going to stir this in.

Now, these tiny little particles of chocolate are going to melt in very easily, and since we haven't really disturbed their structure, the beta crystals are still intact in here, and that's going to set off a chain reaction as the rest of the chocolate cools down, and it's going to help to temper our chocolate.

So if this looks like it's not actually melting all the way, you can always take it back to the microwave -- only for about 5 seconds at a time -- until it is just melted.

All right.

So that is beautiful and glossy and fully melted.

So this is going to go right on the caramel, and it's just a thin veneer of chocolate.

This is not really a chocolate dessert.

It's a caramel dessert.

-It is really fun to watch you make this.

Every layer just looks better and better.

-So good.

All right.

So now I'm going to take an offset spatula.

I love these tiny little ones.

Helps get into all of those little crevices.

And we're going to quickly spread this over the top, getting right to the edges, into the corners.

So this is going to go into the fridge just until the chocolate is set.

That's going to take about 10 minutes.

It's time for the payoff, Julia.

-Yay!

-10 minutes in the fridge, the chocolate is just set, so now we're going to get it out of the pan.

And thanks to the foil sling, that should be very easy.

-I love this sling trick, and it works well for all sorts of bar cookies and brownies.

-There we go.

Peel this back, and now I'm going to lift it up.

If you wouldn't mind taking that foil away.

-You bet.

-Whoo-hoo.

-[ Chuckling ] Ooh.

It's even prettier out of the pan.

-It serves one.

-If only that were true.

-We're going to cut these into smaller pieces because a little bit goes a long way.

And it's very easy to do, but you do want to use a serrated knife.

I like to score through the chocolate first.

So I'm going to cut it width-wise, or across-wise, right in half.

There we go.

So now, each of these gets cut again in half.

Just a little bit of the sawing -- gentle.

And we'll go ahead and cut this one in half, as well.

So now, each one of these gets cut into 10 pieces.

This is where you really want to go slow here.

There we go.

Two for you, two for me, because you're going to say, "Oh, I only want one, Bridget," and then, you're going to say, "Where's my other one, Bridget?"

-These are just beautiful.

I mean, those layers are so nice and even.

And like you said, not a thick layer of chocolate, just that thin veneer on top.

-It's beautiful.

Yeah.

It's just enough of that bittersweet chocolate.

You're going to say it's a perfect combination.

-[ Chuckles ] Mmm.

-Mmm!

-Mmm.

Mmm!

-Shut the door.

-[ Laughs ] This is really good.

It's not only the flavors.

It's the textures.

-Mm-hmm.

-It's the firmness of the shortbread and that caramel layer.

It has the perfect texture.

These are simply amazing, Bridget.

Well done.

-Thank you.

-So if you want to be a millionaire, you have to get your hands a little dirty and use them to press in a quick shortbread crust into a baking pan.

The combination of sweetened condensed milk and heavy cream makes a foolproof caramel layer, and the whole shebang is topped off with a beautiful layer of tempered chocolate.

From our test kitchen to your kitchen, a top-drawer recipe for millionaire's shortbread.

-You feel richer already?

-Mm-hmm.

-Pay you in shortbread.

-Hmm.

Mmm.

♪♪ Some people call them bread knives, but to us, a good serrated knife is for more than just bread alone.

In fact, we use them to cut everything from baguettes and brioche to tender cakes and squishy tomatoes, and Adam is here to tell us which serrated knife sliced through the competition.

-Ooh, good one, Julia.

I like that.

All right.

The point of using a serrated knife... -Oh, good one.

-You get one.

I get one.

There are a couple of reasons you want to use a serrated knife.

Number one is to get good purchase on foods that are squishy or kind of hard.

-Mm-hmm.

-The points will help you get that initial cut going.

Number two is just for good, smooth, friction-free cutting because you have the spaces between the points that reduces the metal on the cutting edge, reduces the friction.

You can see that we have our lineup here of nine serrated knives.

The length of the blade was in the 9- to 10-inch range, because if it's any shorter than 9 inches, you're going to have a tough time cutting a wide loaf of artisanal bread or cutting through, say, a cake layer horizontally.

And the price range was about $20 to about $200.

-Hmm.

-And the tests included cutting through yellow cake layers horizontally, cutting softer breads like challah, cutting firmer breads, like really crusty things like Francese, cutting soft, squishy, ripe tomatoes.

We also cut through some loaded turkey sandwiches that have avocado on them for an extra slip factor.

So the testers actually found that there were two serration styles, and you can see them both here.

The one on the top... -Oh, it's lacy and scalloped.

-It's rounded serrations, whereas the one on the bottom, they're pointed.

-Yeah, and I'd imagine the pointed grabbed better.

-The pointed did a much better job in our tests.

Testers found that the rounded, scalloped serrations had a harder time getting initial purchase on a lot of foods.

-Makes sense.

-And here's something interesting.

Let's step down to this challah.

-Okay.

-One of the things they found is that the greater the number of serrations, actually, the worse the cutting job.

-Huh.

-Try this knife with the wooden handle there.

-All right.

It works okay.

It's not the greatest.

I'm really working at it.

-Yeah.

-If I take a look, there's a lot of crumbs here on the board.

-Right.

-It's a little ragged.

-So why don't you give that second knife a try?

-Okay.

-That first one that you were using has 55 serrations.

The second one that you're going to try now has 33.

-Okay.

Ooh.

It goes through the bread much more easily.

And look.

There's almost no crumbs.

-It's really interesting.

-Yeah.

-It's a lot easier.

It's a little counterintuitive.

-And also, you can see this piece is nice and smooth.

This is kind of hairy looking.

-Yeah.

It's a little ragged.

-Yeah.

It's pretty ragged.

-So, you know, testers looked into this, and what they learned is that when you're pressing down on a knife, the force that you're using to press down on the knife gets spread out among the number of serrations that there are.

So that means the greater the number of serrations, the less cutting force that each one receives, which is why... -Interesting.

-...fewer serrations were better.

Of course, testers also considered the handle.

-Yep.

-There's this term "affordance" that ergonomists use, and it sort of indicates a handle that will allow a wide range of comfortable grips because it's simple.

It's smooth.

It doesn't force your hand into any one position.

-Mm-hmm.

-Check this one out.

-All right.

-See what you think of that.

-Ooh, I don't like it.

It's small.

I'm really having to grip it quite hard, and, actually, it's pinching me right there.

Yep.

That, I don't like.

-That's what the testers thought, also.

This one has less affordance because it's a harder material, and it's got these sharper angles, and it's a little narrower.

Why don't you try this one now?

-All right.

Ooh.

That's comfortable.

It's a little more rounded here through the middle, so I don't actually have to grip it as hard to feel like I have some stability.

-That's a more comfortable handle for everybody in general, and this knife that you just put down, I'm going to give it right back to you.

This is the winning knife.

That is the Mercer Culinary Millennia 10-inch bread knife.

It's got 29 serrations, a lot of space between them.

-Mm, the fewest.

-The fewest of all of them, so it cuts nice and cleanly.

It's got a comfortable handle with good affordance.

And, speaking of affordance, you can afford it because the price is only $22.10.

-Ooh.

-So it was one of the less- expensive knives in the test.

-All right.

So there you have it.

For the best serrated knife, choose a Mercer Culinary Millennia 10-inch-wide bread knife for just $22.10.

♪♪ -Leave it to the French to take a simple butter cake and turn it into something spectacular.

That's what they've done on the coast of Brittany with gâteau Breton.

It's unlike any butter cake you've seen, and we're in great hands today because Elle is going to show us how to make this glorious gâteau Breton.

-Traditionally, this cake is made with a jam or fruit filling in between two firm layers of cake.

-Mmm.

It's so good.

I love this cake.

-It's so good.

So the first thing that we will focus on is the filling.

-Okay.

-So we're going to start with 2/3 cup of water.

Also, 1/2 cup of chopped California apricots.

Now, you can make this with Turkish apricots, if you like, but we prefer the flavor of the California apricot.

-A little bit brighter.

-A little brighter.

-Mm-hmm.

-We're just going to puree this until it's smooth.

It takes about two minutes.

-Okay.

-All right.

That looks great.

It's nice and smooth and has a little bit of texture.

We're just going to add this to a 10-inch nonstick skillet, turn this on to medium heat, and we're going to stir it frequently and let it go for about 10 to 12 minutes.

This looks great.

It's nice and dark in color, and you can pull your spatula through and see that distinct trail.

-Very, very thick, and that is key to this recipe, as you're going to see in a minute.

-All right.

So I'm just going to add this to our bowl.

Oh, this smells so, so good.

So now we're going to add 1 tablespoon of lemon juice to this.

That's all set.

I'm going to put this in the fridge for 15 minutes to cool.

-Sounds great.

-Great.

Okay, Bridget.

So here's the most exciting part about this recipe, for me, is making the cake.

-Yes.

-So here we have 16 tablespoons of butter, and we're going to cream this for one minute on medium-high.

-Okay.

-And so, we're giving this butter a head start because we want to create a dense, crumbly crust, not one that has a lot of air incorporated into it.

-Okay.

-So we're also looking for this butter to become pale and very whippy.

Okay.

So our butter has now creamed for one minute, and we're going to add to this 3/4 cup sugar, plus 2 tablespoons, and let it cream for another three minutes.

All right.

It's been three minutes.

So we're going to add our eggs one at a time.

So we have five egg yolks here, and we're going to just let these go for 30 seconds.

-Okay.

Now, the egg yolks are essential here.

We did not add any egg whites.

Egg whites would do two things.

We want this batter to be really nice and thick, and that would add extra water to the batter.

The egg whites will also provide more lift, and since we want a denser, more crumbly cake, they're not a good idea, so yolks only.

-All right.

That looks great.

It's quite creamed.

I'm just going to scrape the bowl.

To make sure we got all the sugar in there, all the butter incorporated.

Before we move on, I'm going to add 2 tablespoons of rum... -Mmm.

-...and 1 teaspoon of vanilla.

I'm going to just let this mix for one minute.

I'm going to turn this down to low so we can start to add our dry ingredients -- 2 cups of flour, and I'm going to add 1/2 teaspoon of salt.

-A little bit of salt goes a long way -- keeps cakes from tasting too sweet and also just balances out all the flavors.

-All right.

It's been 30 seconds, and already, we have a nice, thick batter that we're looking for to make this cake.

So I'm going to take this paddle off and get all of our batter in here so that we can give it a final stir.

We actually did a really good job mixing.

There's not a lot down in there, but it's always better to check.

-I like that you included me, as in "we."

You did all the work.

-Well, it's a French butter cake.

It's always "oui."

-[ Laughs ] Very good.

-I'm going to add half of this cake batter to this 9-inch cake pan that we've already greased.

So I like to spin the cake pan as I'm spreading out the batter, kind of make sure I get it all evenly distributed.

And it's important that this top layer is even because that's where our jam is going to go, right?

-Okay.

-I think we're all set.

Now, I'm going to put this in the freezer for about 10 minutes, and that's just a little baker's trick that we like to use because if we don't get this batter a little bit more firm, when we put the jam on top, it's just going to sink.

Okay.

So this has been in the freezer for 10 minutes, and as you can see, it's firmed up quite a bit, which is so important when we're putting on our jam filling.

This is about 1/2 cup of our jam mixture.

I'm going to use my spreading method of rotating the pan, and I'm going to leave a 3/4-inch space from the edge of the pan.

All right.

I think we're all set.

-All right.

-And I'm going to put this back in the freezer so that the jam filling can set, also.

-Sounds good.

-Okay, Bridget.

So this has been in the freezer for 10 minutes, and our jam has set.

-Okay.

-So I think it's safe for us to apply the top layer of our cake.

-Sounds good.

-All right.

So this is just the remaining batter from what we used earlier for the bottom of this cake.

All right.

That looks good.

As the French say, c'est bon.

-C'est bon.

-Now, I'm going to use my spinning method for spreading this batter evenly.

Just be gentle with this batter spread so that it doesn't cause your jam to push.

I mean, it's set, but you can't be too aggressive.

-Now, you can really see how thick this cake batter is as Elle is spreading it in there, and it does take a little bit of pushing to get it all towards the side of the pan, but it really has to be this thick in order for the cake to have that ripe, dense texture.

-Now, it's time for the pièce de résistance to beautify this gâteau Breton.

So we're going to start with one egg yolk mixed with 1 teaspoon of water, and we're going to use our pastry brush and just brush this egg wash on top of our French butter cake.

-Now, we think about things like a croissant, a lot of different pastries being brushed with egg wash, but not necessarily a cake, especially cake batter before it's baked, but you'll see this cake is going to bake up with the most beautiful shiny top.

-All right.

That looks great.

So traditional French butter cakes are usually adorned with this beautiful pattern on top.

So we're going to use the tines of our fork.

Start at that three-quarter mark from the edge.

We're going to make three lines, and we're going to make sure they're at least 1 1/2 inches apart.

Great.

So I'm going to turn this to a 45-degree angle, and we're going to do the same thing we just did the first time, and you want to create diamonds.

-We always want diamonds, though.

-They're a girl's best friend.

-Voilà.

-Beautiful diamonds.

-It's time to put this in the oven at 350 degrees for about 45 minutes.

Oh, my goodness.

-Stunning.

And what did I say about that shiny top?

That is beautiful, that egg wash.

Absolutely gorgeous.

-Very traditional.

Tu es belle.

So we can't eat this cake just yet.

It's too hot.

That inside is like lava.

-Quelle tragique.

-Exactly.

So we're going to let it cool here on this cooling rack for 30 minutes.

After that, we're going to use a knife to scale it away from the pan.

We're going to turn it out on the cooling rack and let it cool for one hour.

-Okay.

-Bridget, this cake looks amazing.

Look what we did!

-I feel like I've been waiting 1,000 years for this cake.

I know how good it is, but it never gets old.

-Let's find out right now.

I would say you can share this with your friends, but we probably won't.

-[ Laughs ] -There you go.

-[ Chuckling ] Oh.

Look at that beautiful layer of jam sandwiched perfectly in between those cake layers.

I mean, that's a nice surprise for anyone.

-[ Laughs ] -It's the perfect balance of sweet, and it's got that little bit of tart apricot in it.

This top layer, it's almost like a pie crust, with that little egg wash on top.

It's got a little bit of flakiness to it.

-So delicious and buttery.

-Ugh, perfect.

Elle, this is a most amazing cake.

Thank you so much for sharing it with us.

-It was my pleasure.

Thanks so much.

-Our beautiful cake starts with a homemade skillet apricot jam.

Use egg yolks to create a thick batter, and then, assemble the cake.

Freeze a thin layer of cake batter, jam filling, and more cake batter.

Glaze and score the cake, and then bake until golden brown.

So, from our test kitchen to your kitchen, the elegant and incomparable gâteau Breton.

You can find this recipe, along with all the recipes, tastings, and testings from this season on our website, americastestkitchen.com.

Join us inside the test kitchen at americastestkitchen.com, where you can explore our newest season's recipes, learn about top-performing kitchen equipment, and master cooking techniques alongside your favorite test cooks.

Visit us at americastestkitchen.com/tv.

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