While brownies are cooling begin to make the frosting. In a medium bowl combine butter, milk, cocoa powder, and powdered sugar until a smooth frosting texture is reached. If mixture is too dry add 1 tablespoon of milk at a time. If too runny, add in one tablespoon of powdered sugar at a time.
Once frosting is the right texture spread over brownies while they are still warm so that some of the icing melts into the brownies. Cut into squares and use the foil to help lift the brownies out of the pan.
