Preheat the oven to 250F. Line a large baking sheet with parchment paper.
In a large bowl, whip the egg whites until soft peaks form. While still beating, slowly add in the sugar and continue to beat until thick and glossy. Beat in the vanilla. Sprinkle the vinegar and cornstarch over the top and fold in.
Make 12 equal mounds of the meringue on the prepared baking sheet, keeping them at least 1 inch apart. With the back of a spoon, make a well in the center of each mound.
Bake in the preheated oven for about 1 hour, until the outside is dry. Turn off the oven and let them cool completely in the oven.
Before serving, whip the cream until soft peaks form. Slowly add the powdered sugar and continue to beat until stiff peaks form. Place a dollop of the cream in the center of each pavlova. Top with diced strawberries. Serve immediately.