Preheat oven to 225F. Line a large baking sheet with parchment paper. Using a glass or round cookie cutter as a guide, trace six 3-inch circles on the parchment, spacing them apart. Flip the parchment over so the pencil marks are underneath.
In a large clean bowl, beat the egg whites and cream of tartar with an electric mixer on medium speed until soft peaks form. Gradually add the powdered erythritol one tablespoon at a time, beating on high between each addition.
Continue beating until the meringue is thick, glossy, and holds stiff peaks. Beat in the vanilla extract and white vinegar. Divide the meringue among the six traced circles on the parchment. Use the back of a spoon to shape each mound into a nest, building up the edges slightly higher than the center to create a well for the filling.
Bake for 1 hour and 15 minutes. Turn off the oven and leave the pavlovas inside with the door slightly cracked open until they cool completely, at least 1 hour. This prevents cracking.
When ready to serve, beat the heavy whipping cream with powdered erythritol and vanilla extract until stiff peaks form.
Spoon generous dollops of whipped cream into the center of each pavlova. Top with fresh raspberries, blueberries, and a few mint leaves. Serve immediately for the best crispy-outside, marshmallowy-inside texture.
