Preheat oven to 325°. Beat butter at medium speed with an electric mixer until creamy; gradually add sugar, beating well. Combine flour, baking powder, and salt; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition.
Beat egg whites at high speed until stiff peaks form. Fold one-third of egg whites into batter; fold in remaining egg whites. Spoon batter into 3 greased and floured 9-inch round cake pans.
Bake at 325° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Remove from pans to wire racks, and cool 1 hour or until completely cool.
Spread Lane Cake Filling between layers and on top of cake. Prepare 7-Minute Frosting; spread onto sides of cake.
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