1/2 c. butter
4 tbsp. cocoa
1/3 c. milk
1 lb. confectioners' sugar
1 c. chopped walnuts
1 tsp. vanilla
1/4 c. peanut butter (optional)

Combine butter, cocoa and milk in a saucepan. Cook over medium heat, stirring occasionally until mixture boils. Remove from heat and stir in peanut butter and confectioners' sugar until smooth. Add vanilla and chopped walnuts. Quickly spread over cake. Top with chopped walnuts if desired.