Grease and flour 1 (14-inch) round cakepan; set aside.
Beat shortening and butter at medium speed with an electric mixer until creamy; gradually add sugar, beating until blended. Add eggs, 1 at a time, beating just until blended.
Combine cake flour, baking powder, and salt; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Stir in vanilla.
Beat egg whites at high speed with an electric mixer until stiff peaks form. Fold into cake batter. Spoon batter into cakepan.
Bake at 325° for 1 hour and 20 minutes or until a wooden pick inserted in center comes out clean. Cool cake in pan on a wire rack for 15 minutes; remove from pan, and let cool completely on wire rack.
Wrap layer in plastic wrap, and freeze 2 hours.
Note: One recipe will make 2 (10-inch) layers and 2 (6-inch) layers. Spoon 5 cups batter into each of 2 greased and floured 10-inch round cakepans, and 2 cups batter into each of 2 greased and floured 6-inch round cakepans. Bake the 10-inch layers 30 minutes and the 6-inch layers 22 minutes or until a wooden pick inserted into the center comes out clean. Layers may be frozen up to 1 month. Unwrap and thaw at room temperature 2 hours.