Preheat oven to 180 degrees C. Line a baking tray with baking 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, cornflour, vinegar and vanilla. Spoon in mounded tablespoonfuls onto the baking tray.
Place baking tray into oven and reduce temperature to 120 degrees C. Cook 1 hour. Turn off oven and allow to dry 8 hours, or overnight.