1/2 c. butter
3 1/2 tbsp. cocoa
1/3 c. milk
1 lb. powdered sugar
1 tsp. vanilla

Put butter, cocoa, and milk in a saucepan and let come to a boil. Remove from heat and add powdered sugar and vanilla. Nuts are optional. Pour icing immediately over hot cake as it comes out of the oven.

For variety, put peanut butter in icing.