Beat all ingredients at low speed for 7-10 minutes (10-12 minutes at high speed for portable mixer) until icing forms peaks. Keep icing covered with a damp cloth when not in use.
Yields 3 cups of icing.
Note: Royal icing should have good body and be moderately stiff: It will not create a lasting bond if too runny and soft. For snow, I sometimes add a few drops of Karo Syrup to thin it just a little for a softer look.
Recipe by Recipes Food and Cooking at https://recipesfoodandcooking.com/2015/10/18/halloween-chocolate-gingerbread-house/