2 cups all-purpose flour
1 cup unsweetened cocoa
2 teaspoons baking powder
1 teaspoon baking soda
1/2 teaspoon salt
1 1/2 cups buttermilk
2 teaspoons vanilla extract
2 cups sugar
1 cup margarine or butter (2 sticks), softened
4 large eggs
Preheat oven to 350 degrees F. Grease three 8-inch round or two 9-inch round cake pans, or 13" by 9" metal baking pan. Line bottom(s) with waxed paper; grease paper. Dust pan(s) with flour. Or line thirty 2 1/2-inch muffin-pan cups with fluted paper liners.
On waxed paper, combine flour, cocoa, baking powder, baking soda, and salt. In 2-cup glass measuring cup, mix buttermilk and vanilla. Set aside.
In large bowl, with mixer at low speed, beat sugar with margarine or butter until blended. Increase speed to high; beat until creamy, about 2 minutes. Reduce speed to medium-low; add eggs, 1 at a time, beating well after each addition.
With mixer at low speed, alternately add flour mixture and buttermilk mixture, beginning and ending with flour mixture; beat just until batter is smooth, occasionally scraping bowl with spatula.
Pour batter into pan(s). Bake 45 to 50 minutes for 13" by 9" layers or 30 to 35 minutes for 8- and 9-inch layers, until toothpick inserted in center of each cake comes out with a few crumbs attached. Or, pour batter into muffin-pan cups. Bake 25 minutes. Cool cake(s) in pan(s) on wire rack(s) 10 minutes. Run small knife around sides of pan(s) to loosen cake. Invert cake(s) onto rack(s) to cool completely; discard waxed paper. Or, remove cupcakes from pans and cool completely.
