How to Make It
Heat the oven to 300° F. In a small bowl, combine the vinegar, vanilla extract, and potato starch; set the mixture aside. Combine the egg whites and 1 1/2 cups of the sugar in a large mixing bowl and beat on medium speed until soft peaks form. Add the potato starch mixture and continue beating until the meringue is stiff and glossy. Fold in 1/2 cup of the chocolate chips.
Line a baking sheet with parchment paper. Scrape the meringue onto the center of the pan, using a rubber spatula to shape it into an 8-inch disk. (The meringue will expand as it bakes, so leave a few of inches between the meringue and the edge of the pan.) Place the pan in the oven, reduce the temperature to 250° F, and bake for 1 ½ hours. Turn off the oven and let the pavlova cool to room temperature inside.
Toss the strawberries and raspberries in a medium bowl with the remaining tablespoon sugar, then pile the fruit onto the center of the pavlova. Place the remaining chocolate in a microwave-safe bowl and microwave in 30-second intervals, stirring in between, until melted and smooth. Drizzle over the pavlova just before serving.