In the bowl of an electric mixer, mix the egg whites and vanilla until frothy.
Gradually, add the sugar and mix on low speed until the sugar is incorporated and the icing is shiny. Turn the mixer to med-high and beat until the mixture forms stiff, shiny peaks, approximately 5-7 minutes.
Stir in food coloring if desired.
For immediate use, transfer to a pastry bag fitted with a tip and pipe onto the cookies. (Or if you're using a zip top bag, clip corner and pipe onto cookies.)
Icing can be stored in an airtight container for up to 3 days.
Video
Notes
Consistency: Add more water for thinner flooding icing or more sugar to thicken.
Flavor: Swap almond extract for lemon or peppermint during holidays.
Storage: Refrigerate up to 1 week. Bring to room temp before using.
Vegan option: Replace meringue powder and water with 3 Tablespoons aquafaba.