Preheat the oven to 200°F. Prepare a sheet of parchment paper by tracing a 9" round circle on it and flipping it over onto a baking sheet. You should still be able to see the circle outline through the paper., In a large bowl, beat the egg whites with the salt and cream of tartar on medium-high speed until soft peaks form., Combine the sugar and cornstarch and gradually add it to the whites with the mixer running. The mixture will thicken and turn glossy. Beat for 1 more minute., Spread the meringue into a round on the parchment, using the circle as a guide. Mound the outside edges higher to make a shallow "bowl.", Bake for 1 hour. Turn off the oven and leave the door closed. Leave the meringue in the oven for at least 1 hour, or as long as overnight; it will color slightly from white to light tan (small cracks are normal)., Up to an hour before serving, combine the heavy cream with the confectioners' sugar and whip until thickened. Add the vanilla. Spoon the whipped cream into the center of the cooled pavlova and top with sliced fresh fruit., Store refrigerated for up to one day; once filled, the meringue will soften quickly.