Preheat your oven to 325°F. Line a large baking sheet with parchment paper. Trace an 8" cake pan with chalk or a pencil in the center of the parchment paper, then flip the paper so the drawn-on side faces down.
In a heat-proof bowl, whisk to combine the egg whites, sugar, and vanilla. Place the bowl over a small saucepan with 2 inches of simmering water. *** Cook the mixture while whisking constantly until the sugar is fully dissolved.
6 large egg whites, 1 ¾ cups superfine sugar **, 1 tsp vanilla extract
Pour the egg white mixture into the bowl of a stand mixer fitted with a whisk attachment. Beat the egg whites on high until stiff peaks start to form, about 4 minutes.
Reduce the mixer's speed to low and add the cornstarch and the lemon juice. Increase the speed to high and mix for a minute more.
2 tsp corn starch, 1 tbsp lemon juice
Pile the finished meringue into the center of the circle you traced earlier. Form the meringue into a cake-like shape. Then, using an offset spatula, draw the edges toward the center in a series of swoops.****
Transfer the pavlova to the oven and immediately reduce the temperature to 225°F. Bake for 2 hours, then turn the oven off and leave the pavlova to rest in the oven for another 2 hours. Do not open the oven door at any point during the baking and resting process. *****