Preheat oven to 120°C (fan 100°C). Line a baking tray with baking paper and draw a 22–24cm circle as a guide.
Place egg whites into a stand mixer and set aside.
In a saucepan, combine caster sugar and water. Bring to a boil over medium heat and cook until the syrup reaches 115–118°C (soft-ball stage).
When the syrup reaches temperature, start whisking the egg whites on medium speed.
Slowly pour the hot sugar syrup into the egg whites in a thin stream while continuing to whisk.
Increase speed to high and whisk for 6–8 minutes until thick, glossy and completely cool.
Gently fold in vinegar, cornflour and vanilla.