Shilpa Uskokovic’s Chocolate Sheet Cake with Brown Butter Frosting

CAKE

1. Place a rack in middle of oven; preheat to 375°. Line the bottom of a 13 x 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, 1 3/4 cups (219 g) all-purpose flour, and 1 teaspoon baking soda in a medium bowl to combine.
2. Whisk 3/4 cup (64 g) Dutch-process cocoa powder, 3/4 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, 3/4 cup well-shaken buttermilk, 2 teaspoons Diamond Crystal or 1 1/4 teaspoon Morton kosher salt, and 2 teaspoons vanilla extract and whisk again just to combine.
3. Add dry ingredients to cocoa mixture and whisk gently until just combined and batter is smooth. Scrape batter into prepared pan.
4. 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.

FROSTING AND ASSEMBLY

1. Cook 1/4 cup (1/2 stick) unsalted butter, room temperature, in small skillet over medium-low heat until it begins to foam; add 1/3 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 2/3 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.
2. Using an electric mixer on medium-high speed, beat 2 1/2 teaspoons Diamond Crystal or 1 1/2 teaspoon Morton kosher salt, 1 teaspoon 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 ounces powdered sugar, sifted, and beat, starting on low speed, until well combined, about 1 minute. Add brown butter mixture and remaining 8 ounces powdered sugar, sifted, and beat until frosting is light and fluffy, about 2 minutes.
3. Spread frosting evenly over top of cake, working all the way to the edges. Using a spoon, create decorative divots and swirls in frosting if desired. Sprinkle with flaky sea salt (if using) and sprinkles.

Do ahead: Frosting can be made 2 days ahead. Cover and chill. Bring to room temperature, then beat until fluffy again before using.

— Recipe from Bon Appétit