Bake and cool 1-layer cake 1 1/2 in. high. Cut in half, stack halves with icing and position cut side down on foil-wrapped board cut to fit (allow space on ends for clouds). Ice cake smooth; mark 3/8 in. wide divisions for rainbow with toothpick. Cover rainbow sections with tip 16 stars. Print tip 4 name. Pipe tip 12 ball clouds.