Preheat the oven to 250F/120C and line a baking sheet/tray with parchment paper.
Whisk the egg whites in a clean bowl at medium speed until they form medium-stiff peaks. You want them to hold their form fairly well, but don't over-beat.
Gradually add the sugar 1a spoonful at a time, beating in after each addition, until it is all added and the mixture is glossy. Make sure it is well mixed in and test by rubbing a small amount between two fingers - if it feels gritty, the sugar is not all dissolved so mix a bit longer.
Add the cornstarch and vinegar, and whisk in to combine. If needed, dot a small amount under the corners of the parchment paper to hold it in place. Then form four even mounds on the parchment. Smooth each of them out to be a relatively even circular shape, still relatively high, then form a slight indent in the middle of each.
Bake in the preheated oven, in the middle of the oven, for approximately 40-50 minutes until it they are dry to touch and just starting to color slightly. It will seem crisp when touched (although be gentle so you don't break it). Turn off the oven and leave the pavlovas inside with the door closed for a further 1 hour or more. This will help avoid them weeping and cracking (though a little cracking is fine, you will cover a lot when you top them)
Shortly before serving, whip the cream until it forms medium-firm peaks.
Top each pavlova with some lemon curd, cream and optionally some fruit to decorate on top - blueberries, as I have used here, work well, but raspberries or strawberry would also be good. You could also top with a few candied nuts eg almonds.