Preheat oven to 400 degrees. Line two baking sheets with baking parchment and set aside.

Beat egg whites and salt in small bowl at high electric-mixer speed until frothy. With mixer still at high speed, add sugar gradually and continue beating until meringue peaks stiffly (about 4 minutes). Beat in vanilla, then by hand fold in lemon zest.

Drop meringue from rounded teaspoon onto prepared baking sheets, spacing 2 inches apart. Set in oven, immediately turn oven off, and let cookies remain in the oven for 2 hours (you can leave them in overnight)

Peel meringue off parchment and store in airtight container.

Makes about two dozen cookies.

Note: A cookie contains 23 calories, 0 g fat, 0 g cholesterol and 17 mg sodium