Grease and flour a 15 1/2" x 10 1/2" x 1 1/2" jelly roll pan. Follow the directions for a chocolate cake mix and pour mixture into the pan. Bake at 400 degrees for 20 to 25 minutes.

Five minutes before the cake is done, start the topping.

In a saucepan, melt 1 cube (1/2 cup) butter. Add 6 tablespoons milk and 4 tablespoons unsweetened cocoa. Bring to a boil; stir.

Remove from heat. Stir in 1 pound box powdered sugar, 1 cup chopped walnuts and 1 tablespoon vanilla. Stir until smooth and syrupy. If the powdered sugar doesn't blend well with the other ingredients, return mixture to heat and stir.