Preheat the oven to 150C/300F. Lightly grease a round baking tray and line it with baking paper. The grease will stop the paper slipping around as you try to shape your pav.
Clean all your utensils scrupulously with hot water and dish soap. Rinse them thoroughly to rid them of all soap residue. Either allow to dry on their own (not touching anything) or dry them thoroughly with a clean, dry tea towel.
Separate the egg whites and yolks in two clean, dry bowls. Add each egg white straight into the mixer so you don’t accidentally contaminate it with egg yolk.
Once you’ve got all your egg whites in the mixer, use the balloon whisk attachment to whisk them for 3 minutes on a medium speed (I use speed 3-4 on my KitchenAid). I found that if I stopped whisking the egg whites just before I thought they were at soft peaks, my meringue was less likely to leak sugar.
So, just before soft peaks, start adding the caster sugar, one tablespoon at a time. I set a timer for 20 second intervals, but you don’t have to be that rigid.
Tablespoon by tablespoon, incorporate all of the sugar. It should take you around 10 or so minutes. During this time, it should start to become shiny and thickened.
Once you have incorporated all the sugar, continue beating on a low-medium speed until you can rub a bit of meringue between your fingers without feeling any sugar granules. For me, this took around 10-15 additional minutes, but it might take less for you.
Once you can no longer feel any sugar granules, add your lemon juice or vinegar and beat just to combine. Then add the cornflour and do the same – just a few spins of the mixer to combine it all.
Use a clean silicon or offset spatula to pour the mixture onto the baking sheet. Shape it however you fancy, keeping in mind that taller pavlovas are more prone to collapse (and have more chewiness in the centre).
Place the pavlova into the oven and turn the heat down to 120C/250F. Cook for 1 hour and 30 minutes, or until the pav can be lifted off the baking paper with no issue. Once ready, allow it to cool in the oven with the door closed – the gentle cooling helps prevent it from cracking.