A hint of lemon makes this royal icing perfectly sweet and sour. It tastes delicious atop one of our cookie recipes.
Put egg whites in the bowl of an electric mixer fitted with the whisk attachment; beat until stiff peaks form. Add sugar, lemon, and juice; beat 1 minute. If too thick, beat in more egg whites; if too thin, beat in more sugar.
Divide icing into small bowls and tint with a few drops of liquid food coloring as desired. Use immediately.