Preheat oven to 350°F. Prepare the white cake mix according to the package instructions. Divide the batter into 5 bowls. Add the food coloring of your choice and mix well. I used red, orange, yellow, green and blue. Place the colored batter in gallon sized resealable plastic bags, cut a small corner and pipe the batter in rows onto a parchment lined 15"x18" half sheet pan or cookie sheet with raised edges. The rows should be touching. Then bake for about 8-10 minutes. Do not overbake. Let cool completely. Use a shamrock shaped cookie cutter to cut your cake into cookies.

Grease and line a 10"x5" loaf pan with parchment paper, then prepare the batter from the chocolate cake mix. Pour a little in the bottom prepared pan. Line up your cookies, so that they are standing upright and right next to each other. They should be touching. Keep adding cookies until the pan is full of cookies from left to right. Pour the rest of the batter over the top of your colorful cookies. Bake for about 45 minutes or until a toothpick inserted in center comes out clean. Let cool. Frost the cake with buttercream frosting. Add sprinkles for more color and have fun cutting into this beauty!

Beat softened butter on medium speed with an electric or stand mixer. Beat for 3 minutes until smooth and creamy. Add powdered sugar, cream, and vanilla extract with the mixer running. Increase to high speed and beat for 3 minutes. Add more powdered sugar if frosting is too thin or more cream if mixture is too thick. Add green food coloring and mix completely.