This fabulous peanut butter fudge frosting uses cocoa powder and peanut butter for a rich taste. It's the perfect finish for any cake. This is a simple buttercream, with peanut butter and cocoa powder added. The cocoa powder adds a wonderful depth of flavor and the cocoa does not make the frosting gritty since it dissolves well in the milk. Make sure that you beat this frosting really well. In fact, it's very difficult, if not impossible, to overbeat it The more you beat it the smoother and more velvety it will become. This recipe will frost a 9" X 13" Sheet cake, a 9" Or 8" Round two-layer cake, or 24 cupcakes.