This flavorful frosting is quick and easy to make, with butter, milk, cocoa, and sugar, and it is not overly sweet. It's a nice frosting to make for cupcakes or a layer cake. Fill a layer cake with jam or whipped cream and cover the top and sides with this cocoa frosting. The frosting is thickened with a flour and milk mixture, which makes it less sweet than a typical powdered sugar frosting. Make sure you beat it long enough to dissolve the sugar or the frosting will be grainy.