Line a baking sheet with a silicone baking mat or parchment paper.
Whisk sugar and cornstarch in a bowl. Set aside.
Beat egg whites in a bowl until they are foamy and have a thick, ribbony texture, 2 to 3 minutes.
Pour 1/4 of the sugar mixture into the egg whites; whisk until completely incorporated, about 30 seconds. Repeat for the rest of the sugar mixture, whisking after each addition, until all of the sugar mixture is incorporated and the egg whites are glossy and thick.
Pour vanilla and vinegar into egg white mixture; whisk until you can lift your beater or whisk straight up and the egg whites form a sharp peak that holds its shape, 2 to 3 minutes.
Spoon egg white mixture onto prepared baking sheet; spread out into a 2-inch high by 6-inch wide disc.
Bake in the preheated oven for 1 hour.
Turn off the oven, crack open the oven door and let the Pavlova cool for one hour.
Whip cream, sugar, and vanilla extract in a bowl until soft peaks form, 3 to 4 minutes.
Transfer Pavlova to a serving plate. Top with whipped cream and fresh strawberries.