I've seen those done with either icing (Canadians don't say "frosting," lol), or Cool Whip, with sprinkles. Another thing you can do is do the reverse, and fill a cupcake liner with ice cream, freeze it solid, and put icing and sprinkles on top so it looks like a cupcake.....but they should be served with spoons, so people don't hurt their teeth biting into them.