Potato Chocolate Cake
["3/4 cup butter or margarine, softened", "2 cups sugar", "4 eggs, separated", "1 cup mashed potatoes", "1/2 cup water", "1 tsp. vanilla extract", "2 cups all-purpose flour", "3 Tbsp. baking cocoa", "2 tsp. baking powder", "1 cup chopped nuts", "1 (16 oz.) can chocolate frosting"]
["In a large mixing bowl, cream the butter and sugar.", "Add the egg yolks, potatoes, water and vanilla; mix well.", "Combine the flour, cocoa and baking powder; add to the creamed mixture.", "In a small mixing bowl, beat egg whites until stiff peaks form; fold into batter along with nuts."]
["butter", "sugar", "eggs", "potatoes", "water", "vanilla extract", "flour", "baking cocoa", "baking powder", "nuts", "chocolate frosting"]