Preheat your oven to 250°F. Line a baking sheet with parchment paper. Using a pencil, trace a 9-inch circle, or four 4-inch circles, on the parchment. Flip the parchment over.
In the bowl of a stand mixer, combine egg whites and a pinch of salt. Whisk on high speed until stiff peaks form (4-5 minutes).
Reduce mixer speed to medium and slowly add the sugar over 2 minutes. Stop and scrape down the sides of the bowl.
Increase speed to high and whisk until the mixture is smooth, glossy, and very stiff peaks form (6-7 minutes).
Decrease speed to low. Add vanilla, vinegar, and cornstarch, mixing just to combine.
Gently spoon the meringue onto the traced circle(s) on the parchment, spreading to fit the shape and forming a slight well in the center. Place in the preheated oven and bake for 45 minutes.
Turn off the oven heat. Leave the meringue inside for 3 hours, or until it's crisp and dry on the outside. Open the oven door and let the pavlova cool completely before removing (approximately 30 minutes).
Just before serving, top the cooled pavlova with the macerated fresh summer fruit. If desired, add warmed preserves sauce, chopped pistachios and a dollop of fresh whipped cream for a simple yet elegant topping.