If you’d like to use homemade buttercream, make two batches of Food Network Kitchen’s Vanilla American Buttercream recipe. [https://www.foodnetwork.com/recipes/food-network-kitchen/vanilla-american-buttercream-3326387] If you are unable to find metallic jelly beans, you can substitute yellow, blue and orange mini candy-coated chocolates, such as M&M’s Minis.