From my friend the master baker, the best frosting ever. Fantastic with white, chocolate or lemon cake, or the lemonade cupcakes here: http://www.food.com/recipe/lemonade-cupcakes-95878/review#rz-w This one could make your reputation.
In the bowl of an electric mixer fitted with the paddle attachment, whip butter for 8 minutes on medium speed (I use “4″ on my KitchenAid). Butter will become very pale & creamy. Add remaining ingredients and mix on low speed for 1 minute, then on medium speed for 6 minutes. Frosting will be very light, creamy, and fluffy. Best used right away.