On those occasions when you find yourself with extra egg whites left over from a recipe calling for yolks, don't throw them away or give them to the dog: make meringues, those light as air, nonfat cookies that go together in a flash, then crisp up ever so gradually in a slow oven.
Preheat the oven to 250°F. Lightly grease, or line with parchment, two large baking sheets.
In a large bowl, beat the egg whites until foamy, then add the salt and cream of tartar.
Add the sugar gradually, continuing to beat, until the meringue is thick and glossy, and forms stiff peaks.
Stir in the vanilla or other flavoring.
Drop meringue by tablespoonfuls (a tablespoon cookie scoop works well here) onto the prepared baking sheets. Alternatively, use a piping bag with a star tip to pipe them onto the baking sheets. Sprinkle each with sparkling sugar crystals.
Bake for 1 hour, then turn off the oven and let the kisses cool in the unopened oven (don't peek!) for 2 1/2 to 3 hours (1 1/2 to 2 hours for meringues that are chewy in the center, rather than crisp all the way through).
Store, airtight, at room temperature for up to a month.
For a festive holiday look, dip the base of the cooled meringues in tempered chocolate, then in a shallow dish of nonpareils before the chocolate sets.
