The Cook's Illustrated Cookbook (311 page)

WHY THIS RECIPE WORKS

This easy wartime cake made with just a few ingredients (flour, sugar, cocoa powder, baking soda, vanilla, and mayonnaise, a stand-in for butter and eggs) had a lot of good things going for it, but chocolate flavor wasn’t one of them.

Our first order of business was deepening the chocolate flavor. More than a half-cup of cocoa turned the cake dry and chalky so we supplemented the cocoa powder with a little melted chocolate. “Blooming” the cocoa powder in hot water intensified its flavor, and using hot coffee instead of water enriched the flavor even more. Chopping the dark chocolate fine meant we could melt it in the hot coffee as well—no need for an extra pan. As for the oddball ingredient—mayonnaise—we wondered if we could make the cake richer by replacing it with eggs and butter or eggs and oil. These cakes weren’t as moist and velvety as the mayonnaise version. Why? We learned that mayonnaise contains lecithin, an emulsifier that helps keep the oil suspended in micro-droplets. These small droplets greatly aid the oil’s ability to coat the flour’s protein particles, leading to a supremely tender cake. Yet, while butter and oil were out, the egg was a keeper, as it helped create richer flavor and a springier texture.

SERVES 8

Any high-quality dark, bittersweet, or semisweet chocolate will work in this recipe. Instead of confectioners’ sugar, the cake can be served with
WHIPPED CREAM
.

1.
Adjust oven rack to middle position and heat oven to 350 degrees. Grease 8-inch square baking pan, line with parchment paper, grease parchment, and flour pan.

2.
Whisk flour, sugar, baking soda, and salt together in large bowl. In separate bowl, combine cocoa and chocolate. Pour hot coffee over cocoa mixture and let sit, covered, for 5 minutes. Gently whisk mixture until smooth, let cool slightly, then whisk in mayonnaise, egg, and vanilla. Stir mayonnaise mixture into flour mixture until combined.

3.
Scrape batter into prepared pan and smooth top with rubber spatula. Bake cake until toothpick inserted in center comes out with few crumbs attached, 30 to 35 minutes.

4.
Let cake cool in pan on wire rack, 1 to 2 hours. Dust with confectioners’ sugar, if using, cut into squares, and serve straight from pan; alternatively, turn cake out onto serving platter, dust with confectioners’ sugar, if using, and serve.

WHY THIS RECIPE WORKS

Sheet cakes, for all their simplicity, can still turn out dry, sticky, or flavorless and, on occasion, can even sink in the middle. We wanted a simple, dependable recipe, one that was moist yet also light and chocolaty.

We started with the mixing method, testing everything from creaming butter to beating egg yolks, whipping egg whites, and gently folding together everything in the end. The best of the lot was the most complicated to make, so we took a step back. The simplest technique we tried was simply whisking all the ingredients together without beating, creaming, or whipping. The recipe needed work, but the approach was clearly what we were after. We added buttermilk and baking soda to lighten the batter, and we reduced the sugar, flour, and butter to increase the chocolate flavor. To further deepen the chocolate taste, we used semisweet chocolate in addition to the cocoa. We baked the cake at a low temperature for a long time—40 minutes—to produce a perfectly baked cake with a lovely flat top. Though this cake can be frosted with almost anything, we like a classic American milk chocolate frosting, which pairs well with the darker flavor of the cake.

SERVES 15

We prefer Dutch-processed cocoa for the deeper chocolate flavor it gives the cake. The baked and cooled cake can also be served with lightly sweetened whipped cream or topped with any frosting you like in lieu of the milk chocolate frosting. This frosting needs about an hour to cool before it can be used, so begin making it when the cake comes out of the oven.

CAKE

FROSTING

1. FOR THE CAKE:
Adjust oven rack to middle position and heat oven to 325 degrees. Grease 13 by 9-inch baking pan, line with parchment paper, grease parchment, and flour pan.

2.
Sift flour, cocoa, and salt together into medium bowl; set aside. Microwave chocolate at 50 percent power for 2 minutes; stir, add butter, and continue heating until melted, stirring once every additional minute. Whisk eggs, sugar, and vanilla together in medium bowl.

3.
Whisk chocolate into egg mixture until combined. Combine buttermilk and baking soda; whisk into chocolate mixture, then whisk in dry ingredients until batter is smooth and glossy. Pour batter into prepared pan and smooth top with rubber spatula. Bake cake until firm in center when lightly pressed and toothpick inserted in center comes out clean, about 40 minutes. Let cool on wire rack until room temperature, at least 1 hour.

4. FOR THE FROSTING:
Microwave cream, corn syrup, and salt in bowl until simmering, about 1 minute, or bring to simmer in small saucepan over medium heat. Place chocolate in food processor. With processor running, gradually add hot cream mixture, then process for 1 minute. Stop processor, add confectioners´ sugar, and process to combine, about 30 seconds. With processor running, add butter, 1 piece at a time, then process until incorporated and smooth, about 20 seconds longer. Transfer frosting to medium bowl and let cool at room temperature, stirring frequently, until thick and spreadable, about 1 hour. Spread frosting over cake and serve.