Cream together butter and sugar. Sift together flour and baking powder and add to creamed mixture alternately with milk and vanilla. Fold in egg whites. Pour into three 9" round layer cake pans. Bake in moderate oven (350°) 30 to 35 minutes, until golden brown. Cool on racks. Spread Raisin/Nut Filling between cooled layers. Frost sides and top of cake with Southern Frosting.