Royal icing goes on smooth but dries hard, making it an excellent glue for adding edible decorations to your favorite baked creation. Traditionally, the icing relied on egg whites to stiffen it up so it could adhere well, but meringue powder is an egg-free alternative that still hardens quickly and completely. The basic icing is white, but you can substitute liquid food coloring for some of the water if you want to tint your icing glue.
Meringue Powder Method
Sift confectioner's sugar to remove any lumps. Mix 1½ tablespoons of meringue powder into every 1/2 pound of confectioner's sugar.
Mix in water 1 tablespoon at a time, whisking the icing until it is smooth and free of lumps. Substitute up to 1 tablespoon of lemon juice for some of the water to cut the sweetness in the icing.
Add more sugar, a tablespoon at a time, if the icing is too runny, or add water a drop or two at a time if it's too thick. Mix and adjust until the icing is soft enough to spread or pipe but no longer runny enough to pour off a spoon.
Traditional Method
Sift and measure 4 ounces of confectioner's sugar, or about 1½ cups, for every egg white you are using. Place the measured sugar in a bowl.
In another bowl, whisk the egg white with water or lemon juice, using 1 tablespoon for every egg white.
Mix the egg mixture into the sugar. Whisk everything together until smooth, then add more sugar or water until the icing is at the desired consistency.