- 3/4 cup water
- 1 cup unsweetened cocoa powder
- 3/4 cup buttermilk
- 1 3/4 cups all-purpose flour
- 3/4 teaspoon baking powder
- 1/2 teaspoon baking soda
- 1/2 teaspoon salt
- 1 1/2 cups (packed) golden brown sugar
- 1/2 cup mayonnaise
- 1 large egg
- 1 large egg white
- 1 teaspoon vanilla extract
- Creamy Chocolate Frosting
- Position rack in center of oven; preheat to 350°F. Butter two 9-inch-diameter pans with 1 3/4-inch-high sides. Dust with flour; discard excess. Bring 3/4 cup water to boil in medium saucepan. Remove from heat. Whisk in cocoa to form paste. Cool slightly. Add buttermilk; whisk until blended.
- Whisk flour and next 3 ingredients in medium bowl to blend. Using electric mixer, beat sugar and next 4 ingredients in large bowl until light, about 5 minutes. Beat in cocoa mixture. Add dry ingredients and beat just until blended. Divide batter between prepared pans.
- Bake cakes until tester inserted into center comes out clean, about 20 minutes. Cool cakes in pans on rack 10 minutes. Turn cakes out onto racks; cool.
- Place 1 cake layer on platter. Spread 3/4 cup frosting over. Top with second layer. Spread remaining frosting over entire cake. (Can be made 1 day ahead. Cover with cake dome; let stand at room temperature.)