Flower Power Cake

First, frost the 13- by 9-inch cake with the white icing. (Tester's Tip: To avoid dark crumbs in the light-colored icing, we used a white cake and cupcakes.) Arrange the cupcakes and mini cupcakes (you can cut them in half horizontally for thinner flowers if you wish) on top of the cake, wherever you'd like a flower. Cover them with the white icing as well, including the sides. Using a pastry bag (or a plastic bag with one small corner cut off), pipe a green icing stem for each flower. If you'd like, you can also add green gel icing grass. Place spearmint leaves along the icing stems, then decorate the cupcakes with colored sugar and candies to create a garden of colorful blooms. You can also pipe on dollops of icing, as we did with some of our flowers.