Preheat your oven to 350°F and prepare a large baking sheet with parchment paper. Draw six 4-inch circles on the paper, then flip it over and secure it with masking tape.
Using a stand mixer or hand mixer, beat the egg whites, cornstarch, and salt on high speed until foamy. Gradually add the sugar, one tablespoon at a time, and continue beating until the mixture is thick and glossy. This may take 8-10 minutes.
Mix in the vanilla extract until fully incorporated.
Divide the meringue mixture evenly among the drawn circles on the parchment paper. Use the back of a spoon to shape each mound into a nest with a slightly indented center and 1-inch sides.
Slide the baking sheet into the oven, then immediately reduce the temperature to 300°F. Bake for 1 hour without opening the oven door.
Turn off the oven and leave the meringues inside to cool completely—this helps prevent cracking. Allow at least 4 hours, or let them sit overnight if possible.
Carefully peel the meringue nests off the parchment paper. Assemble each pavlova by adding 1/4 cup whipped cream to the center of each meringue and topping with sliced strawberries and kiwis.