Ingredients in royal icing include 3 ounces of pasteurized egg whites, 1 teaspoon of vanilla extract and 4 cups of confectioners' sugar. Place the egg whites and the vanilla in the bowl of a stand mixer, and beat until the mixture is frothy.
Gradually add the sugar, and mix on low speed until it's well-incorporated and the mix is shiny. Turn the speed up to high and beat until it forms stiff peaks. Add food coloring if desired. If the icing isn't for immediate use, put it in an airtight container and store in the fridge for up to three days. If you're going to use it right away, transfer the icing into a pastry bag or snip the corner off a storage bag and add the icing.
Martha Stewart's royal icing calls for the whites of 2 large eggs, or more if the icing is too thick, 4 cups of sifted confectioners' sugar, or more if the icing is too thin, the juice of 1 lemon and 3 drops of glycerin. You can also substitute 5 tablespoons of meringue powder and 1/3 cup of water for the raw eggs. Beat the whites until stiff but not dry. Add the sugar, lemon juice and glycerin and beat together for one more minute.