Bake a white cake using any recipe or box mix. Allow to cool fully. Gather colored icing in each color of the rainbow (available in the baking aisle of the grocery store), white frosting, a paper template of a four-leaf clover and gold sanding sugar.
Apply a layer of purple icing to the top of the cake layer on the plate. Top with another layer of cake and then apply a layer of blue icing.
Continue the icing/cake layering process until each color of the rainbow is present and the topmost layer of cake is on top of the red icing. Chill in the fridge to firm.
Once the crumb coat is set, apply a thicker coat of frosting. Then pour a small amount of gold sanding sugar into a bowl. Make sure to have the paper clover template on hand.
Pour the sanding sugar into a fine mesh sieve. Then, holding the paper template over the center of the cake, shake the sieve gently to sprinkle sugar over the top of the cake.