1. Heat oven to 350 degrees F. Coat 13 x 9 x 2-inch baking pan with nonstick cooking spray. Line bottom of pan with waxed paper. Coat paper with nonstick cooking spray.
2. Beat butter in medium-size bowl until smooth. Beat in sugar until light and fluffy, about 3 minutes. Beat in eggs, one at a time, beating well after each addition.
3. Whisk together flour, baking powder and salt in small bowl. On low speed, alternately beat flour mixture with milk into butter mixture in 3 additions, beginning and ending with flour. Stir in vanilla, lemon extract, lemon rind and lemon juice. Pour into prepared pan, spreading to level.
4. Bake in 350 degree F oven for 34 minutes or until toothpick tests clean. Cool cake in pan on wire rack 10 minutes. Invert cake onto rack; remove pan and waxed paper. Let cool completely.
5. Place cake, right side up, on cutting board. With serrated knife, trim top level, if needed. Trim uneven or sloping sides. Cut cake into sixteen 3-1/3 x 2-1/4-inch rectangles. Using white icing (1/2 cup total), frost sides (not tops) of cakes with skim coat to smooth any crumbs and rough edges.
6. Remove all traces of foiI top from one container of lemon icing. Microwave on high for 45 seconds, stirring at 15-second intervals, until icing is pourable.
7. Place skim-coated cakes on wire rack over jelly-roll pan. Pour about 3 tablespoons melted lemon icing over each cake, allowing to dribble down sides. If icing in container begins to harden, microwave again for 15 seconds. Using a knife or small spatula, smooth icing on cakes. Refrigerate for 10 minutes.
8. Lift wire rack off pan. Scrape up as much icing as possible from pan, and transfer to second container of lemon icing. Repeat Steps 6 and 7, melting lemon icing and pouring over cakes until a smooth layer is achieved. Refrigerate 20 minutes to firm icing.
9. Divide remaining white icing into fourths in 4 separate bowls. Leave 1 bowl white; tint one bowl pink, one purple, and the last one blue. Transfer to 4 pastry bags fitted with writing tips, or to heavy-duty plastic food-storage bags with a small corner snipped off and then fitted with writing tips. Decorate cakes by piping on butterflies, dragonflies and other whimsical insects. Makes 16 cakes.