Preheat oven to 225°F/107°C.
Combine sugar and cornstarch in a bowl and give it a stir. Set aside.
In a stand mixer bowl fitted with a whisk attachment (or use an electric hand mixer), add in the room temperature egg whites and sea salt.
Whip beginning on low speed, until the egg whites become foamy.
Add in the cream of tartar/lemon juice/vinegar.
Gradually increase the speed and slowly add in the cornstarch and sugar mixture, about 1 tablespoon in at a time.
When it reaches soft peaks, add in the vanilla extract.
Whip until the egg whites become shiny and reach stiff peaks.
Divide the whipped meringue into 4 mounds onto a large baking sheet lined with parchment paper.
With the back of a spatula or spoon, add a divot to the centre of each mound.
Bake the pavlova at 225°F/107°C for 1 hour. Do not open the oven at any point in the baking process.
Turn off the oven and let the pavlova remain in the oven until fully cool, at least 3 hours.
When removing the pavlova, they should easily come off the parchment paper and are completely dry to the touch.
If the pavlova are not completely dry, re-bake them at 220°F/104°C for another 10-15 minutes, until crisp and dry.