1. Beat egg whites until stiff, but not dry. Add confectioners' sugar and lemon juice. Beat for 1 minute or more. If icing is too thick, add more egg whites; if it is too thin, add more sugar.
2. For a glossy icing, mix in a few drops of glycerin. To tint icing, add food coloring sparingly, one drop at a time, using the end of a toothpick. Blend well.
To ice the entire cookie, use a pastry bag with a #2 tip. A thinner icing consistency is preferable when flooding; just add a bit of water to thin out the icing. Fill the pastry bag, cuff the open end over one hand, and use a spatula to scrape in the icing. Twist the half-full bag closed, so the icing doesn't leak out at the top.
Using a #3 tip, rest the tip on your index finger, pushing the icing out gently with your thumb.
Dust the cookie with sanding sugar to make it sparkle. Tap off the excess sugar when the cookie is dry.