Preheat the oven to 110°C. Line a large baking sheet with baking parchment.
Make sure your bowl and whisk of your stand mixer are clean - you can do this by rubbing them with a cut lemon or some vinegar on a piece of kitchen paper.
Add the sugar, egg whites, cream of tartar, vinegar and vanilla to the stand mixer and whisk - starting on low to make sure no big air bubbles form, then increase the speed to medium and beat for 4-5 minutes until the egg mixture has come to soft peaks.
Add the caster sugar 1 tablespoon at a time until all incorporated. You should end up with extremely thick, glossy and stable meringue with proper stiff peaks.
Add the cornflour, then whisk to combine.
Drizzle over the melted chocolate over the surface of the meringue, then gently fold through the mixture - be careful not to over-do it, we want it rippled, not incorporated!
Use your finger or a teaspoon to use a tiny bit of the meringue mixture to affix your baking parchment to the baking sheet, then use two spoons to scoop the mixture into little mounds on the baking tray - you can make a little dip in the top if you’d like them to hold cream as mini pavlovas. If you’re not happy with your chocolate rippling, try just drizzling some chocolate over the top.
Bake for 1 hour until the outer shell is crisp to the touch and the meringue should easily unstick from the baking paper - you can check the base by feeling that it seems dry.
Allow to cool either in the switched off oven, or on a wire rack.
Serve with lightly whipped cream, berries & chocolate.