1/2 cup plus 1 tablespoon meringue powder*
1 cup plus 2 tablespoons warm water
12 cups icing (confectioners')sugar
3/4 teaspoon cream of tartar
*Meringue powder can be purchased at health and bulk food stores. It may also be called dried egg whites. The royal icing can vary depending on the brand of meringue powder used and the humidity; it may be necessary to thin the icing with an additional tablespoon of warm water or thicken it with additional icing sugar to make the desired consistency. If the icing is going to be used for piping, it should be thinned to the consistency of molasses.