Separate the eggs and measure 150ml/150grams of egg whites. Set them aside and allow to come to room temperature.
Pre-heat the oven to 150 °C (302 F) and line a baking tray with baking paper. Place a small amount of oil spray underneath the paper to stop it from sliding.
Using a 20cm plate or cake tin, trace a 20 cm/8 inch circle onto the middle of the baking paper.
Using a clean, dry bowl and electric stand mixer, beat the egg whites at low-medium speed for around five minutes, until the whites are white, foamy and forming soft peaks.
While beating, slowly add the caster sugar, one tablespoon at a time.
Once all of the sugar has been added, increase the speed to medium-high (not top speed) and continue beating for around 3 minutes, until the egg whites are thick, glossy and form stiff peaks. *By this stage, the sugar should have dissolved. You can test this by pinching a little of the egg whites between your fingers. The mixture should not feel gritty. If it does, beat for a further minute until the mixture is smooth.
Decrease the speed to low and add the cornflour and vinegar. Mix only until combined and then turn off the mixer. Don't overbeat.
Working quickly, use a spatula to gently add the meringue to the centre of the circle on the lined baking tray. Use the circle as a guide to gently coax the meringue to size. Smooth (or sweep) the sides and level the top of the pavlova.
Place the pavlova in the oven and immediately turn the temperature down to 100°C (212 F). Bake for 1 hour and 30 minutes (without opening the oven door), until the shell of the pavlova is crisp. Turn the oven off and leave the oven door closed. Leave the pavlova to cool completely in the oven, overnight or for at least six hours.