1 cup butter or margarine, softened
2 cups sugar
1 cup firmly packed brown sugar
6 eggs, separated
2 1/2 cups all-purpose flour
1/2 cup cocoa
1 cup commercial sour cream
1/4 teaspoon baking soda
1 teaspoon vanilla extract
Cream butter; gradually add sugars, beating well at medium speed of an electric mixer. Add egg yolks, one at a time, beating after each addition.
Sift flour and cocoa together. Combine sour cream and baking soda. Add flour mixture to creamed mixture alternately with sour cream, beginning and ending with flour mixture. Mix just until blended after each addition. Stir in vanilla.
Beat egg whites (at room temperature) until stiff peaks form; fold into batter. Spoon batter into a greased and floured 10-inch tube pan. Bake at 325 for 1 hour and 15 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes; remove from pan and let cool completely on a wire rack.
