This Swiss buttercream is light, fluffy, and almost whipped cream-like. If I could only eat one frosting for the rest of my life, it would probably be this one. This recipe is a scaled-up version of Deb Perelman's from Smitten Kitchen: http://smittenkitchen.com... —Catherine Lamb
enough to decorate a three-tier wedding cake
Whisk the egg whites and sugar together in a metal bowl over a pot of simmering water, until the sugar dissolves and the egg whites are warm to the touch. If you're worried about salmonella, make sure to heat the egg whites to 160° F -- don't let it get hotter than that, or your eggs will scramble.
Pour egg white mixture into an electric mixer, and turn up speed to high. Whip until the egg whites are light, glossy, and doubled in size. Add in vanilla.
Add in softened butter, one stick at a time, whipping thoroughly after each addition. Whip until Swiss buttercream is thick, shiny, and resembles cream cheese. Do not lose faith if this takes a long time -- just keep whipping!
Frosting will keep in a sealed container for up to one week. Let come to room temperature and re-whip before frosting your cake.