although there are many recipes for royal icing, i have found one that works every time and hardens nicely so that cookies can be stacked, packaged or transported for gift giving.
here is the recipe: 5 1/4 cups confectioner’s sugar, 1 tablespoon and 1 1/2 teaspoons cream of tartar, and 1/2 cup egg whites (refrigerated egg whites work fine)
measure and incorporate all ingredients. combine with a hand mixer on low speed, then switch to high for 2-5 minutes until they are snow white and fluffy. keep the icing bowl covered with a damp towel while decorating cookies or a gingerbread house. this icing recipe will not soak into the cookie making it soft or causing a gingerbread house to collapse.
this recipe can be made in smaller quantities. this recipe is enough to decorate one gingerbread house.