1/4 cup unsweetened cocoa powder
1/4 cup boiling water
2 cups sugar
1/2 cup (1 stick) butter, softened
1 cup (8 ounces) sour cream
1-1/2 teaspoons vanilla extract
1 teaspoon baking soda
2 cups all-purpose flour
1/2 teaspoon salt
5 egg whites
2 (16-ounce each) cans chocolate frosting
1. Preheat oven to 350 degrees F. Grease and flour two 9-inch round cake pans.
2. Combine the cocoa powder and boiling water in a small bowl and stir until the cocoa is dissolved.
3. In a large bowl, combine the sugar and butter. Beat with electric mixer until light and fluffy, 1 to 2 minutes. Add the cocoa mixture and beat 1 minute longer. Beat in the sour cream, vanilla and baking soda. Add the flour and salt; mix 1 minute more.
4. In a medium bowl, beat the egg whites until stiff peaks form, 2 to 3 minutes. Fold into the batter.
5. Spoon 1/2 the batter into each prepared cake pan. Bake 25 to 28 minutes or until a toothpick inserted into the middle comes out clean. Transfer to wire racks to cool. Cut each cake layer into 2 even layers for 4 total layers. Spread the frosting between the layers and over the top and side of the cooled cake. Makes 12 to 16 servings.