In a large mixing bowl, stir together the powdered sugar, meringue powder, and cream of tartar.
Add the warm water and vanilla extract to the dry ingredients.
Beat with a mixer on low speed until well combined.
Increase the mixer speed to high and beat for 7 to 10 minutes, or until the icing is very stiff and forms peaks.
If you're not using the icing immediately, cover the bowl with a damp paper towel and then tightly wrap it with plastic wrap.
Royal icing dries out quickly when exposed to air.
You can chill the royal icing in the refrigerator for up to 48 hours.
Before using it, make sure to give it a good stir.
Notes / Tips / Wine Advice:
This recipe yields approximately 3 cups of royal icing.
Note:
Meringue powder is a mixture of pasteurized egg whites, sugar, and edible gums. It is essential for making Royal Icing that dries quickly with a smooth, hard finish. You can find it in the baking aisle of large supermarkets or in the cake decorating department of hobby and crafts stores.