There are many recipes for brownie sheet cake icing, but one popular recipe calls for mixing together 1/2 cup of butter, 1/4 cup of unsweetened cocoa powder, 3 tablespoons of milk, and 1 teaspoon of vanilla extract. Then, gradually add in 2 cups of powdered sugar until the mixture is smooth.
BRING MARGARINE, COCOA AND MILK TO A BOIL.
BE CAREFUL NOT TO SCORCH.
REMOVE FROM HEAT AND ADD SUGAR NUTS VANILLA AND BUTTER FLAVORING.
SPREAD GENTLY OVER CAKE AS SOON AS IT IS REMOVED FROM THE OVEN.