This is the wonderful frosting for the amazing sugar cookies my mom makes every year. It is from the same Betty Crocker Cookbook.
Vanilla Butter Frosting
1/3 cup soft butter or margarine
3 cups confectioners' sugar
1 1/2 teaspoons vanilla
About 2 tablespoons milk
Blend butter and sugar. Stir in vanilla and milk; beat until frosting is smooth and of spreading consistency.