Preheat the oven to 250 degrees F (120 degrees C). Line a baking sheet with a silicone baking mat or parchment paper.

Whisk sugar and cornstarch together in a bowl. Beat egg whites in a second bowl until foamy with a thick, ribbony texture, 2 to 3 minutes. Whisk in 1/4 of the sugar mixture until completely incorporated, about 30 seconds. Repeat with the remaining sugar mixture, whisking after each addition, until all is incorporated and egg whites are glossy and thick.

Add 1 teaspoon vanilla and vinegar; whisk until you can lift the beater or whisk straight up and egg whites form a sharp peak that holds its shape, 2 to 3 minutes.

Spoon egg white mixture onto the prepared baking sheet; spread out into a 2x6-inch disk.

Bake in the preheated oven for 1 hour. Turn off the oven, crack open the oven door, and let the Pavlova cool for 1 hour.

Transfer cooled Pavlova to a serving plate.

Whip cream, sugar, and remaining 1 teaspoon vanilla in a bowl until soft peaks form, 3 to 4 minutes. Spread over Pavlova and top with fresh strawberries.