This royal icing recipe is from "Martha Stewart's Cookies" and is used to decorate Jewel Heart Cookies.
Place confectioners' sugar, meringue powder, and water into the bowl of an electric mixer fitted with the whisk attachment; beat on low speed for 10 minutes. Use immediately, or store in an airtight container up to 2 days (icing hardens quickly when exposed to air). Beat well with a rubber spatula before using.