An icing that dries hard, so you can use it to glue pieces together, or use as a flat surface to decorate. Add less sugar to make it thinner and pour over cookies or petits fours; add more sugar to make it more thick for spreading or piping. It will be stiff enough to decorate over within about half an hour, and it will be like cement in four hours.
In an electric mixer with a whisk attachment, whisk the egg whites on high until they are opaque and foamy.
Add the sugar a little scoop at a time, continuing to whisk on high. Add the lemon juice.
Keep whisking on high until the icing is as thick as you want it. Adjust how much sugar you add to make it as thick as you want.
Keep the icing covered tightly, with plastic wrap touching the icing, until you're ready to use it because it starts drying out immediately.