Preheat oven to 300° F and line a baking sheet with parchment paper.
In a large bowl using a hand mixer, beat egg whites with a large pinch of salt until foamy. While beating, slowly add in sugar and beat until meringue is thick and glossy, about 7 minutes. Beat in cornstarch, vinegar, and vanilla.
Pile meringue in the center of prepared baking sheet and use a spatula or spoon to spread into an 8″ circle. Make a small well in the center.
Place meringue in the oven and immediately reduce temperature to 250°. Bake until set but still white, about 1 hour and 15 minutes.
Turn off oven and let pavlova cool completely in oven, at least 2 hours and up to overnight.
Transfer cooled pavlova to a serving dish and top with whipped cream and berries.