Chocolate Sheet Cake with Brown Sugar Buttercream Frosting

I love making homemade cake, but it is so disappointing to make a cake and then realize that a cake mix would have been better.  I have made cakes that are too dry, too wet, too crumbly, not sweet enough, you name it.  And those box mix cakes have gotten better over the years, so it's not that easy to stay a step ahead.

But when we made this chocolate sheet cake from America's Test Kitchen, we knew we had a winner.  Everyone needs a perfect, chocolate cake recipe in their repertoire, and this is ours.  It has a nice crumb and a deep chocolatey flavor.  We have used it for numerous birthday cakes, and it is dense enough to hold up to a bit of rearranging if you have a request for, say, a wizard's hat cake.

 
If you do cut and reshape it, I highly recommend that you first pop it into the freezer for about half an hour.  This firms the edges up just enough to make the cutting and frosting easier and fewer crumbs end up working their way into the final product. 

The frosting that I have made to accompany this cake is Gourmet's Brown Sugar Buttercream frosting.  Yes, yes, it involves a candy thermometer, a stream of hot sugar syrup, and an obscene amount of butter, but it is worth it.  Every bite.  And for me one of the thrills of cooking is that there is always a new challenge to conquer.  Consider it extreme cooking. 

As you might imagine, the frosting is rich and buttery as a good buttercream should be, and the brown sugar gives it a caramel flavor.  I have used the frosting on chocolate and vanilla cakes and it pairs well with either.  Despite the dark brown sugar, the frosting is also light enough in color that it can be tinted to suit your child's whim.

Second Helping (from the archives):  Vanilla Bean Pudding

Chocolate Sheet Cake with Brown Sugar Buttercream Frosting

The cake can be  wrapped in plastic wrap and stored at room temperature for up to 2 days.  The frosting will keep in the refrigerator for 1 week or in the freezer for 1 month.  Before using it, bring it to room temperature and beat it with a mixer until it is smooth again (the butter may separate a bit over time).

Adapted from America's Test Kitchen and Gourmet
Serves 10 to 12
30 minutes preparation time for cake
40 minutes baking time for cake
1 hour preparation time for frosting

For the cake:
12 tablespoons (1 1/2 sticks) unsalted butter
8 ounces semisweet chocolate, roughly chopped
3/4 cup cocoa, preferably Dutch processed
1 1/4 cups unbleached all purpose flour
1/2 teaspoon baking soda
1/4 teaspoon salt
4 large eggs
1 1/2 cups granulated sugar
1 teaspoon vanilla extract
1 cup buttermilk

for the frosting:
3 large egg whites, left at room temperature for 30 minutes
1/8 teaspoon salt
1 cup packed dark brown sugar
1/2 cup water
1/2 teaspoon freshly squeezed lemon juice
3 sticks unsalted butter, cut into 10 or so pieces and softened
2 teaspoons vanilla extract

First, make the cake.  Position an oven rack in the middle of the oven and preheat the oven to 325 degrees.  Generously butter a 9 by 13-inch baking pan.

In a metal bowl set over a pan of barely simmering water, melt the butter and chocolate.  Set aside to cool slightly.  In a small bowl, sift together the cocoa, flour, baking soda, and salt.  Stir together the eggs, sugar, and vanilla in a separate, larger bowl.  Whisk the buttermilk into the egg-sugar mixture and mix until smooth. 

Whisk the chocolate mixture into the egg-sugar bowl, stirring until it is well incorporated.  Mix in the dry ingredients and whisk until the batter is smooth and glossy.  Pour the batter into the pan and smooth it evenly across the top of the pan.

Bake until a toothpick inserted in the center comes out clean, about 40 minutes.  (If you want to make this cake as a layer cake, it takes about 35 minutes for 2 9-inch round layers to cook).  Cool the cake in the pan for about an hour, then turn onto a cooling rack to cool it completely before spreading on the frosting. 

While the cake is cooling, make the frosting.  Mix the egg whites and salt together in the bowl of a mixer.

Combine the brown sugar and water in a small pot and bring it to a boil over medium-high heat.  As the syrup bubbles onto the sides of the pot, occasionally brush it down with a pastry brush dipped in cold water. 

When the syrup begins to boil, beat the egg whites at medium-high speed.  When the whites begin to get frothy, add the lemon juice.  Turn the mixer down to medium and beat the egg whites until they just form soft peaks.  Let the whites rest until the syrup is ready.

While the whites are mixing, the sugar syrup should be bubbling away.  Boil it until it reaches 238 to 242 degrees on a candy thermometer.  Immediately pour the syrup into a heat-proof measuring cup. 

Begin beating the egg whites again, this time on high speed.  Slowly add the sugar syrup by pouring it down the side of the bowl.  Continue beating the mixture, occasionally scraping down the sides of the bowl, until it is cool to the touch, 6 to 8 minutes.  As tempted as you may be, it is important not to skimp on this step or the butter will not mix into the meringue properly. 

Turn the mixture down to medium and add the butter one piece at a time, mixing until the butter incorporates completely after each addition.  If the mixture looks soupy after adding a few pieces of butter, the meringue is likely not cool enough.  Place the mixing bowl into a larger bowl of ice water for about a minute to cool it, then begin mixing and adding the butter again. 

At some point while adding the butter, the mixture will begin to look curdled and you will think you have made a terrible mistake.  But forge ahead.  By the time all of the butter has been added the mixture will become cohesive again.  Add the vanilla and mix for another minute or two.  Add coloring, if desired, and spread onto the cake.

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Comments

[laura]

that looks so good! i might even get over my fear of candy thermometers to make it.

[Andrea]

A real buttercream is such a joy to work with, it's so worth the effort--and, in my experience, hard to go back once you've learned. I'm always eager for a good buttercream that uses up the whites, since my favorite is a yolk recipe.

[Oscar]

its my 10th birthday cake!!!

[person magical]

it good for you lol