The secret to fluffy frosting is air — and lots of it. Beating your frosting ingredients together at a high speed incorporates air while combining the ingredients. In the case of homemade marshmallow frosting, which contains egg whites, you’ll need to do this beating while the frosting ingredients are gently cooking over a few inches of simmering water.
Things You'll Need
Set a saucepan filled with 2 to 3 inches of water on a burner set to medium-low. Let the water come to a simmer.
Combine the frosting ingredients in the bowl. A typical scratch formula has roughly 2 parts egg whites, 2 parts sugar, 1 part corn syrup, a dash of vanilla extract and a small amount of water.
Place the bowl partially into the saucepan of simmering water so the bowl is not immersed in the water. Use a wire rack if the bowl settles too deeply into the saucepan.
Beat the frosting with a portable beater. Set the speed to medium until the ingredients combine into a soft spread. Turn the mixer to high and continue mixing for several minutes until the frosting becomes thick and fluffy. The entire beating process should take at least six to seven minutes.
Spread the frosting as soon as possible once you’ve finished beating it.
References and ResourcesEpicurious: Devil Dog Cake
Cooking Light: Chocolate Cake With Fluffy Frosting
Epicurious: Ginger-Lime Coconut Cake With Marshmallow Frosting
Duncan Hines: Fluffy Frosting