Preheat oven to 225°F.
Line an un-rimmed (if available) baking sheet with parchment paper. Draw 3½-inch circles on the parchment paper, and turn the paper over so no pencil markings get on the meringue.
In the bowl of a stand mixer fitted with the whisk attachment, whisk the egg whites on high speed until they look like clouds. Keep whisking the whites, adding the sugar slowly until the whites are stiff, glossy, and smooth. Rub a little of the meringue between your finger and thumb – once no sugar granules can be felt, the meringue is ready.
4 large egg whites, 1 cup caster sugar
In a small bowl, mix together the cornstarch, vinegar, and extract. Add this mixture to the beaten egg whites and whisk on high speed for 5 seconds (just until it is incorporated in the whites).
1 teaspoon cornstarch, 1 teaspoon white wine vinegar, ¼ teaspoon pure vanilla extract
Place a tiny dab of meringue under each corner of the parchment to keep it in place. Pile the meringue into the middle of each circle. Gently push the meringue toward the sides to create a rimmed “bowl” of meringue. The sides should be higher than the middle, and the meringue should have a rim to hold the filling. Smooth the middle of each circle with the back of a spoon.
Place meringues in the oven, and reduce the oven temperature to 200°F. Bake for 60 minutes, or until they are firm to the touch and still white. Check on the meringues after the first 15 minutes. If they are darkening or cracking, reduce the oven temperature by 25°F. Once baked, turn off the oven and leave the meringues inside for another hour. Transfer the meringues to a cooling rack to cool completely.
While the meringues cool, pour the cream into a mixing bowl and whisk on medium-high speed for 1 minute. When it begins to thicken, add the powdered sugar and vanilla and continue to whisk just until firm. Do not overbeat (the cream will solidify). Set aside.
1 cup heavy cream, 1 tablespoon powdered sugar, 1 teaspoon pure vanilla extract
Combine all fruit in a bowl and mix gently. Set aside.
1 pint fresh strawberries, ½ pint fresh blueberries, ½ pint fresh blackberries, ½ pint fresh raspberries
Place the jam and lemon juice in a small saucepan. Heat over medium-low heat until the sauce reduces and thickens a bit. If desired, add liqueur and mix.
2 tablespoons fresh lemon juice, 1 cup seedless raspberry or strawberry jam, 1 teaspoon fruit liqueur
Fill each meringue with whipped cream mixture and spread it out to cover the top of each meringue. Be sure to leave a little “bowl” space for the fruit.
Spoon the fruit into the middle of the whipped cream and drizzle the sauce over the Pavlovas. Garnish with mint leaves & sprinkle with powder sugar.