Preheat the oven to 150°C (fan).
Line a large flat baking tray with greaseproof paper. Draw a 20cm round circle in the middle as a guide for how big to make the pavlova.
Separate the eggs with the egg whites in one bowl and the yolks in another bowl. Take extra care doing this to make sure no yolk gets into the whites.Attach the whisk attachment to your stand mixer and make sure the bowl is spotlessly clean and dry. Tip the egg whites into the bowl.Turn your mixer onto a medium-low speed and whisk the egg whites until they reach soft peaks (approx. 6-8 minutes).
Now add 1 tbsp of the castor sugar at a time, counting 20 seconds between each addition. This will take a little while but it’s important to leave enough time for the sugar to dissolve into the meringue before you add the next spoonful. Once all the sugar is added, turn the mixer up to medium speed and whisk for roughly 6 minutes until the meringue reaches stiff peaks. The meringue should stand tall with no curl. Test that the sugar has fully dissolved by rubbing a bit of the meringue between your fingertips, it should feel smooth and not grainy. If it feels grainy, continue to whisk for another minute.
Add the white wine vinegar and whisk into the meringue.
Sift the cocoa powder into the bowl, and very gently fold it into the meringue using a large metal spoon or silicone spatula. You want to avoid folding too many times otherwise all the air will be knocked out, you also want to create a swirly pattern so only fold 4-5 times.
Spoon the meringue onto the baking tray, making a tall mound of meringue in the middle of the circle you have drawn. Use the back of a spoon to shape the meringue into a round shape, making a crater in the middle to hold the filling.
Place on the middle shelf of the oven and immediately turn the temperature down to 130°C (fan). Bake for 80 minutes.
Turn the oven off and leave the door closed. Let the pavlova cool completely inside the oven for at least 4 hours or overnight for best results.