Preheat the oven to 300°F (150°C). Line a baking sheet with parchment paper.
In a clean mixing bowl, beat the egg whites on high speed until stiff peaks form.
Gradually add in the sugar, 1 tbsp at a time, while still beating on high speed.
Once all the sugar is incorporated, add in the white vinegar and vanilla extract and beat for an additional minute.
Scoop the meringue mixture onto the prepared baking sheet and use a spatula to shape it into a large circle, about 1 inch thick.
Create a slight indent in the center of the meringue to hold the whipped cream and berries.
Bake the meringue for 1 hour and 15 minutes, or until it is crispy and lightly golden on the outside.
Turn off the oven and leave the meringue inside to cool for about 1 hour.
In a separate mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
Spread the whipped cream evenly over the cooled meringue, leaving a border around the edges.
Arrange the fresh berries on top of the whipped cream. Add a few mint leaves for garnish if desired.
Slice and serve immediately, or refrigerate until ready to serve.