2 tbsp. all-purpose flour
3/4 c. milk
3/4 c. butter, softened
3/4 c. sugar
1 tsp. vanilla

Combine flour and small amount of milk in saucepan; mix until smooth. Add remaining milk slowly, stirring until smooth. Cook over medium heat until bubbly and thickened, stirring constantly; cool completely. Beat butter and sugar until light and fluffy. Add cooled milk mixture and vanilla; beat until smooth and fluffy. Spread on cooled cake.