Ingredients:
 - 1/2 cup butter
 - 2/3 cup cocoa
 - 3 cups powdered sugar
 - 1/3 cup milk
 - 1 teaspoon vanilla extract

Directions:
  1. In a medium saucepan, melt butter and stir in cocoa.
  2. Alternately add powdered sugar and milk. Beat until light and fluffy.
  3. Stir in vanilla.  If necessary, add a small amount of additional milk.