Beat egg whites in small bowl with electric mixer until stiff peaks form; set aside. Cream sugar and butter in large bowl with electric mixer until fluffy. Add potatoes, vanilla and cocoa. Beat until blended.
Stir in flour, baking powder and soda. Stir in milk and nuts. Carefully fold in egg whites until no white remains. Divide and pour into 2 (8 inch) round cake pans which have been greased and floured. Bake at 350 degrees for 35-40 minutes or until toothpick comes clean. Cool completely. Frost with chocolate frosting.
