Preheat the oven to 120C/250F. Line a large baking tray with tin foil and lightly grease.
In a large mixing bowl, beat you egg whites until stiff peaks form. Using a tablespoon, add the superfine sweetener, until mixed through and glossy. Add the cornstarch, vinegar, and vanilla extract until combined.
Transfer the meringue mixture onto the foil lined sheet. Push together into a circular shape.
Bake the meringue for 90 minutes, or until golden around the sides and tender. Turn the oven off and keep the meringue in there to cool completely. Be sure to leave the door slightly ajar.
Once the meringue has cooled completely, prepare the whipped topping. Beat together the heavy cream and powdered sweetener until thick and smooth. Gently spread over the top of the meringue. Decorate with berries of choice and refrigerate for at least an hour, to set.
