Consider a pavlova bar for your next party, with individual meringue shells, whipped cream, and fresh seasonal fruit (here, we've used blueberries brightened with a touch of lemon zest). Your guests will love assembling their own desserts.
Preheat oven to 250 degrees with racks in the upper and lower third. Using a 3-inch bowl or round cutter, trace 6 circles on each of 2 sheets of parchment paper. Transfer each sheet of paper to a baking sheet tracing-side down.
In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites and a pinch of salt on medium-high speed until soft, glossy peaks form. With mixer running, add granulated sugar 1 tablespoon at a time. Beat meringue on high until stiff and glossy, about 5 minutes more. Sprinkle in cornstarch, vinegar, and vanilla; gently fold to combine.
Using two spoons, scoop a mound of meringue in the center of each of the circles. Use the back of one spoon to create an indentation in the center of each mound. Transfer baking sheets to oven. Bake until firm and dry to the touch but not browned, 35 to 40 minutes. Turn off oven and let meringues cool for 1 hour. Transfer to a wire rack to cool completely.
Whisk cream and confectioners' sugar until soft peaks form. Top meringues with a dollop of whipped cream and a spoonful of blueberries. Sprinkle lemon zest over berries. Serve immediately.
Undressed pavlovas can be kept in an airtight container for up to 1 day.