Separate the egg whites from the yolks (while cold, easier to separate) at least 30 minutes to the night before using them in the recipe. Leave the whites in a covered, clean glass bowl on the counter until ready to use. Save the yolks to use in another recipe.
Preheat the oven to 235˚F/ 113˚C.
On a sheet of parchment paper, draw an 9-inch diameter circle using a pencil for your pavlova outline. Turn the paper upside down with the pencil mark against a baking sheet large enough for the circle.
In a clean glass or metal stand mixer bowl with whisk attachment, whisk the egg whites until soft peaks form (medium speed #4 on KitchenAid mixer). Gradually add sugar, 1 tbsp at time in ~30 second intervals until all is added. Continue to whisk until the sugar has dissolved (check by rubbing mixture between fingers, if grainy, keep whisking).
Once the sugar has almost dissolved and the peaks begin to stiffen (when you lift the whisk, the mixture on the whisk should connect to the bowl mixture), add vinegar slowly while whisking. Slowly add the salt. Then, add in the vanilla a few drops at a time.
Continue whisking until the mixture is shiny and has stiff peaks (the mixture should remain in the whisk and not ooze down). Slowly add sifted cornstarch. You can whisk between medium and high speed (#6-#8 on a KitchenAid mixer). The mixture should hold its shape if mounded and the peaks should stand up without any flopping over.
Scoop the meringue in the circle on parchment paper. Spread the meringue to fill the circle. The outer edge of the meringue should be 2 1/2-3 inches tall with a very shallow well in the center to hold the toppings. For a decorative meringue, use the back of a spoon and make upward motions to form decorative sides on the edges. Smooth the top of the peaks into the meringue. You can also scoop half of the mixture on the circle and pipe the other half on the outer edges for that decorative look.
Bake for 2 hours. Turn off the oven and turn on the oven light. Leave the Pavlova untouched in the oven without opening the oven door and let it stay there overnight.
I don’t recommend opening the oven at all, but if you absolutely have to check, the internal marshmallow should reach 175˚F/80˚C for it to be completely baked. You could use a thermometer and stick it in the center to check the temp (the hole left from the thermometer will be covered with whipped cream and fruit).
When ready to serve, whip the cream in a stand mixer on speed #4 until frothy. Slowly add the sifted powdered sugar and whisk until soft peaks form (they’ll have a soft curl at the peak). Whisk in vanilla until well combined. Spoon the whipped cream on top of the meringue. Top with sliced or diced fresh fruit.
Serve immediately or store in the fridge for up to one day. It’s best eaten immediately on the day it’s made as the top begins to sink and crack from the weight of the cream and fruit.