Preheat oven to 300°F (150°C), line baking sheet with parchment, draw 9-inch circle
Beat egg whites until soft peaks form, gradually add sugar until glossy stiff peaks
Fold in vanilla, vinegar, cornstarch gently
Spoon mixture onto circle, shape well in center
Reduce oven to 225°F (110°C), bake 1 hr 15 min, let cool inside oven
Whip cream with sugar + vanilla until soft peaks
Transfer pavlova, spread cream, top with berries & mint
Serve immediately for best texture