Coat 3 (8-inch) round cakepans with cooking spray; line with wax paper. Set prepared pans aside.
Beat butter and shortening at medium speed with an electric mixer until fluffy; gradually add sugar, beating well. Add eggs, 1 at a time, beating until blended after each addition.
Combine flour, baking powder, and salt. Combine buttermilk and next
3 ingredients. Add flour mixture to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Spoon batter into prepared pans.
Bake at 350° for 24 minutes or until a wooden pick inserted in center comes out clean. (Layers will be thin, about 1 1/4 inch thick.) Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks.
Slice cake layers in half horizontally to make 6 layers. Place 1 cake layer, cut side up, on a cake plate. Spread with 1/3 cup Clear Lemon Filling. Place a second cake layer, cut side down, on top of filling; spread with 1 cup Seven-Minute Icing. Repeat procedure with remaining 4 layers, ending with icing on top. Frost sides of cake with remaining icing; sprinkle with 1 cup coconut.
Note: For testing purposes only, we used 7-UP lemon lime soft drink. Add the soft drink to buttermilk just before using in recipe so it doesn't go flat.