Preheat the oven to 300°F (150°C). Line a baking sheet with parchment paper.
In a clean, dry bowl, beat the egg whites using an electric mixer until soft peaks form.
Gradually add the granulated sugar, one tablespoon at a time, while continuing to beat the egg whites. Continue beating until the mixture is glossy and forms stiff peaks.
Sift the cocoa powder over the egg white mixture and add the white vinegar, cornstarch, and vanilla extract. Gently fold the ingredients together until well combined.
Spoon the mixture onto the prepared baking sheet, forming small mounds to create mini pavlovas. Use the back of the spoon to create a well in the center of each pavlova.
Bake in the preheated oven for about 30-35 minutes or until the pavlovas are crisp on the outside. The centers should still be soft. Turn off the oven and leave the pavlovas in the oven with the door slightly ajar for an additional 15-20 minutes.
Fill each mini pavlova with whipped cream. Spoon over passion fruit puree and top with pickled blackberries, dust with powdered sugar, and garnish with mint sprigs. Serve immediately.