Pre heat the oven to 130C/110C Fan/Gas 3 and draw a 20cm/ circle on the bottom side of a sheet of baking paper.
Pour the egg whites into large bowl or stand mixer bowl. Whisk the eggs whites on a medium speed for around a minute, until the eggs are frothy and still wet. They shouldn't be able to form peaks, if they are stiff and look like clouds you’ve gone too far.
Add a table spoon of caster sugar and whisk on medium speed for 2 minutes. Repeat until all the sugar has gone.
It’s important to add the sugar slowly on a medium speed to allow the sugar to fully dissolves without over whipping the eggs. Get this wrong and your pavlova will weep and is more likely to crack. Set a time for 2 minutes every time you add sugar and whip on a medium setting.
When all the sugar has been mixed in, your egg whites should be smooth, glossy and thick with plenty of volume (like shaving foam). Mix the corn flour with the vinegar to make a paste, then add to the egg whites and whisk on medium for around 2 minutes more minute.
Rub a little mixture between your fingers, it’s should be smooth and velvety. If it’s grainy, mix on medium for another couple of minutes to ensure the sugar has dissolved.
Blob a little bit of mixture on the bottom of each corner of the baking paper to stick it to a baking tray.
Spoon the mixture around the inside of the circle on the baking paper, then fill the middle. Smooth around the outside and level the top with the back of a spatula. It should look like a frosted cake. Then use the tip of the spatula to create vertical ridges by dragging the spatula from the bottom of the pavlova to the top. Repeat all the way round then level off the top. Ridging the sides will create a dome effect when topped with cream and berries. The ridding supports the structure. Make sure your pavlova is no higher than 5cm, any higher and it's like to sink and crack.
Bake in the middle of the oven for an hour then turn the oven off and let it cool completely before removing. Removing too soon will crack the pavlova.
It’s best to make the pavlova the night before and allow to cool in the oven over night. Carefully remove the baking paper, place on a serving plate and store in a cool dry place in an airtight container until ready to decorate. To prevent it going soggy only decorate when ready to serve. Once decorated you can refrigerate for up to a day but it may go soft.