1. Beat butter at medium speed with an electric mixer until fluffy; gradually add sugar, beating well. Add egg yolks, one at a time, beating after each addition.
2. Combine flour and baking powder; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Stir in 1 tsp. vanilla.
3. Beat egg whites and salt at high speed with an electric mixer until stiff peaks form. Stir about one-third of egg whites into batter; fold in remaining egg whites. Spoon batter into 3 greased and floured 9-inch round cake pans.
4. Bake at 350° for 18 to 20 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks.
5. Spread Lemon Filling between layers. Spread Fluffy White Frosting on top and sides of cake. Sprinkle top and sides with coconut; garnish, if desired.
Note: Boxwood is poisonous if ingested. If boxwood sprigs are used as garnish, cut small circle of heavy-duty plastic wrap, and position in center of cake before arranging sprigs and cranberries on top of cake. Remove garnish before serving.