To create a nutritionally sound layer cake that's moist and tender with luscious frosting, we use a combination of full-fat (butter), reduced-fat (1/3-less-fat cream cheese), and fat-free (egg substitute) ingredients. As with any baked good--especially one that's light--measure all ingredients carefully. Twisted lemon and lime slices are a pretty garnish that indicates the flavor of the dessert.
To prepare the cake, coat 2 (9-inch) round cake pans with cooking spray; line bottoms of pans with wax paper. Coat wax paper with cooking spray.
Place granulated sugar and butter in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add egg substitute and the next 3 ingredients (through 1 tablespoon juice); beat well. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt, stirring well with a whisk. Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture. Spoon batter into prepared pans; tap pans once on countertop to remove air bubbles.
Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on a wire rack 10 minutes; remove cakes from pans. Carefully peel off wax paper. Cool completely on wire racks coated with cooking spray.
To prepare icing, place 1 teaspoon lemon rind and next 3 ingredients (through cream cheese) in a medium bowl; beat with a mixer at medium speed until smooth (about 1 minute). Gradually add powdered sugar, beating at low speed just until blended (do not overbeat). Cover and chill for 30 minutes.
Place 1 cake layer on a plate; spread with 1/2 cup icing. Top with remaining cake layer. Spread remaining icing over top and sides of cake. Chill 1 hour. Store cake loosely covered in refrigerator.