Preheat oven to 350 degrees F (175 degrees C). Line a cookie sheet with parchment paper.
In a large glass bowl, beat the egg whites with an electric mixer until soft peaks form. Gradually beat in sugar until firm peaks form. Fold in lemon zest, salt, cornstarch, vinegar, and vanilla. Spoon in mounded tablespoonfuls onto the cookie sheet.
Place cookie sheet into oven and reduce temperature to 250 degrees F (120 degrees C). Cook 1 hour. Turn off oven and allow to dry 8 hours, or overnight.
