Chocolate Sheet Cake

Ingredients

• 2 teaspoons neutral oil, for the pan
• 2 cups (240 g) all-purpose flour
• 1 3/4 cups (350 g) granulated sugar
• 1 cup (84 g) unsweetened natural cocoa powder, divided: 3/4 cup (63 g) for cake and 1/4 cup (21 g) for frosting
• 1 1/2 teaspoons baking powder
• 1 teaspoon baking soda
• 1 teaspoon fine salt, divided: 3/4 teaspoon for cake and 1/4 teaspoon for frosting
• 2 large eggs
• 1 cup (240 ml) buttermilk
• 1/2 cup neutral oil
• 2 teaspoons vanilla extract or alcohol-free vanilla flavoring labeled for 1:1 substitution, divided equally between cake and frosting
• 1 cup (240 ml) hot water
• 1/2 cup (113 g) unsalted butter, softened for frosting
• 2 cups (240 g) confectioners’ sugar
• 3 tablespoons whole milk

Method

1. 1

   Step 1. Allow about 2 hours 40 minutes: 30 minutes hands-on work, 35–40 minutes baking and 90 minutes cooling. Use a 9-by-13-inch metal pan at least 2 inches deep, bowls, whisk, electric mixer and rack. Heat the oven to 350°F. The cake must be completely cool before frosting; soften the frosting butter during cooling. For repeatable results, weigh the flour; if using cups, spoon it in lightly and level without packing.

2. 2

   Step 2. Grease the pan with the 2 teaspoons oil. Whisk the flour, granulated sugar, 3/4 cup cocoa, baking powder, baking soda and 3/4 teaspoon salt in a large bowl.

3. 3

   Step 3. Whisk the eggs, buttermilk, 1/2 cup oil and 1 teaspoon vanilla in another bowl. Stir into the dry ingredients, then carefully whisk in the hot water until smooth. The batter will be thin. Pour into the pan; do not taste raw batter.

4. 4

   Step 4. Bake for 35–40 minutes, until the center springs back gently and a skewer emerges without wet batter. Cool the cake in its pan on a rack for about 90 minutes, until no warmth remains. Cut the frosting butter into small pieces and allow about 30 minutes to soften during this cooling period.

5. 5

   Step 5. For the frosting, beat the softened butter until smooth. Sift in the confectioners’ sugar and remaining 1/4 cup cocoa. Add the remaining 1/4 teaspoon salt, 1 teaspoon vanilla and the 3 tablespoons milk. Beat on low until incorporated, then on medium for 2 minutes until spreadable.

6. 6

   Step 6. Spread over the cooled cake and cut into 16 pieces. Refrigerate the covered frosted cake within 2 hours, or 1 hour above 90°F; let individual slices stand briefly before serving if desired. Keep at 40°F or below and use within 3 days.