How to Make It
In a large bowl, beat the egg whites at medium speed until foamy. Add the confectioners' sugar, 1 cup at a time, beating between additions until the sugar is completely incorporated. Add the lemon juice and beat at high speed until the icing holds its shape, about 5 minutes. Thin with water as needed.
If you have any concerns about eating uncooked eggs, you can make this icing using pasteurized egg whites or powdered egg whites or with an instant royal-icing mix.