[header] How to make rainbow frosting [title] Beat the butter in a large bowl using an electric mixer. [step] Blend and cream well on a medium setting, mixing until the butter is fully whipped, taking about 2-3 minutes. [title] Pour in the powdered sugar. 
[step] Slowly blend in the powdered sugar on low speed. Blend until the frosting becomes stiff, taking about 2-4 minutes.