This "American-style buttercream" isn't a true buttercream, since it doesn't use egg whites. But it's a simple, basic frosting, good for spreading on cupcakes or in-the-pan cakes. It goes together quickly and spreads easily.
In a large bowl, beat together the butter, shortening, and salt till fluffy.
Add about half the confectioners' sugar, and beat slowly until well blended.
Add the vanilla and half the milk or cream, and beat until fluffy.
Continue mixing in sugar and milk alternately until they've been completely incorporated.
Beat until the frosting is light and fluffy.
