Recipe (12-16 servings, about 1 3/4 cups):
Powdered sugar - 3 cups
Butter or margarin, softened - 1/3 cup
Vanilla - 1 1/2 tsp
Milk - 1-2 tbsp
Mix powdered sugar and butter in medium bowl with spoon or with electric mixer on low speed.
Stir in vanilla and 1 tbsp of the milk.
Gradually beat in just enough remaining milk to make frosting smooth an spreadable.
If frosting is too thick, beat in more milk. If frosting becomes too thin, beat in a small amount of powdered sugar.
Generously frosts a 13" by 9" cake or frosts and fills an 8" or 9" two-layer cake.
Source: Betty Crocker Ultimate cake mix cookbook.