This sugary icing makes a great topping for cookies, but it can also be used to decorate cupcakes and cakes. It dries to a hard, white, shiny gloss; food coloring can also be added.
Recipe from Food & Wine
1 egg white
1/2 pound confectioners' sugar (2 1/4 cups)
1 tablespoon water
Spoon the icing into a piping bag fitted with a plain tip and use at once; thin with water if necessary.