6 tbsp. butter
3/4 tsp. vanilla
1 egg yolk
1 1/2 tbsp. peanut butter
2 1/2 c. powdered sugar
1 1/2 tbsp. milk

Cream butter with peanut butter and vanilla. Gradually add the powdered sugar, beating well after each addition. Beat in the egg yolk. Beat in enough of the milk until frosting is of spreading consistency. Enough to frost one 8 or 9 inch square cake.