Chocolate Sheet Cake With Brown Butter Frosting

Come for the chocolate sheet cake recipe—no mixer needed! practically one bowl! big chocolate flavor!—stay for the brown butter frosting. The delicate nutty taste of brown butter shines through this rich buttercream due to dry milk powder, commonly found in the baking aisle of almost every grocery store. Toasted until deeply golden, milk powder becomes a concentrated source of milk solids (the same component responsible for brown butter’s signature taste), making the flavor that much bigger, bolder, and better.

Stirring the cocoa powder with hot water before whipping it into the cake batter does two important things: 1. The heat “blooms” the powder, bringing nuanced flavors to the surface; and 2. It sidesteps the need to sift your cocoa, an extravagantly messy and annoying step. You’re welcome.

Place a rack in middle of oven; preheat to 375°. Line the bottom of a 13×9″ metal baking pan with parchment paper. Lightly coat paper and sides of pan with nonstick vegetable oil spray. Vigorously whisk 2 cups (400 g) granulated sugar, 1¾ cups (219 g) all-purpose flour, and 1 tsp. baking soda in a medium bowl to combine.

Whisk ¾ cup (64 g) Dutch-process cocoa powder, ¾ cup vegetable oil, and 1 cup hot tap water in a large bowl until cocoa is fully dissolved, about 30 seconds. Add 2 large eggs, ¾ cup well-shaken buttermilk, 2 tsp. Diamond Crystal or 1¼ tsp. Morton kosher salt, and 2 tsp. vanilla extract and whisk again just to combine.

Add dry ingredients to cocoa mixture and whisk gently until just combined and batter is smooth. Scrape batter into prepared pan.

Bake cake until it springs back when gently pressed or a tester inserted into the center comes out with a few moist crumbs attached, 25–30 minutes. If serving cake directly from pan, let cool in pan, about 1 hour. If you prefer to serve cake unmolded, let cool in pan 10 minutes. Invert onto a wire rack and let cool completely. Peel away parchment; invert cake, right side up, onto a platter.

Cook ¼ cup (½ stick) unsalted butter, room temperature, in small skillet over medium-low heat until it begins to foam; add ⅓ cup (32 g) nonfat dry milk powder and cook, stirring constantly with a heatproof rubber spatula, until mixture turns a dark nut brown color (milk powder will clump; that’s okay), about 5 minutes. Remove from heat and immediately add ⅔ cup heavy cream (this will prevent further cooking); stir vigorously until smooth (some small flecks may remain and that is okay). Let brown butter mixture cool, about 30 minutes.

Using an electric mixer on medium-high speed, beat 2½ tsp. Diamond Crystal or 1½ tsp. Morton kosher salt, 1 tsp. vanilla extract, and remaining 1 cup (2 sticks) unsalted butter, room temperature, in a medium bowl until smooth and creamy, about 1 minute. Add 8 oz. powdered sugar, sifted, and beat, starting on low speed, until well combined, about 1 minute. Add brown butter mixture and remaining 8 oz. powdered sugar, sifted, and beat until frosting is light and fluffy, about 2 minutes.