Turn the oven off, leave the oven door slightly ajar, and let the meringue cool completely in the oven, 1 to 2 hours. When the meringue is cool, remove pan from oven, carefully removing meringue from the parchment paper. (If planning to use the meringue right away, meringue should be placed directly on a serving dish. (If your meringue attains a few cracks, or sinks a bit in the middle, do not be alarmed. This is normal. If everything goes right, the meringue shell should be firm and crisp on the outside and soft and marshmallowy on the inside.) Alternatively, meringue may be stored in a cool, dry place, in an airtight container, for up to three days.
Chill the clean bowl of an electric mixer and the whisk attachment in the freezer for 10 minutes. Place the sugar in the mixing bowl, adding the cream and vanilla. Beat on high speed until medium peaks form, about 1 minute; do not overbeat or your whipped cream will turn into butter.
Mound whipped cream into completely cooled meringue shell. Top whipped cream with berries. If desired, dust with confectioners’ sugar and garnish with a fresh mint sprig. Cut into wedges and serve. This dessert does not hold well, so plan to enjoy it shortly after it has been assembled. Makes 8 servings.