Preheat oven to 300F(150C).
Draw a 7-inch circle on waxed paper or baking parchment and place on a baking sheet. Beat the egg whites in a mixer bowl until soft peaks form.
Add the sugar gradually, beating constantly until very stiff peaks form.
Beat in the vanilla, vinegar and cornstarch. Spread or pipe mixture inside circle, forming a depression in the center.
Bake at 300F/150C for 1 hour or until firm. Turn off the oven, leaving the meringue to cool in the oven.
Invert the meringue and remove the waxed paper. Place right side up on a serving plate.
PREPARE TOPPING JUST BEFORE SERVING:.
Whip cream with sugar. Spoon it into the depression in the meringue and arrange the berries on the top to serve. Sprinkle nuts and coconut flakes over top, and garnish with mint, if using.