This is a boiled fudge-like icing
1 In a saucepan, combine sugar, cocoa powder, milk, butter and vanilla. Bring to a rolling boil, stirring constantly, and cook for 1 minute. Remove from heat. Using an electric mixer, beat icing for 3 minutes, or until mixture cools and thickens to spreading consistency. Spread onto completely cooled cake.
Does this harden?