Preheat oven to 250 degrees F (130 degrees C) and place rack in center of oven. Line a baking sheet with parchment paper and draw a 7 inch (18 cm) circle on the paper.
In the bowl of your electric mixer, with the whisk attachment, beat the egg whites on medium-high speed until they hold soft peaks. Start adding the sugar, a tablespoon at a time, and continue to beat until the meringue holds very stiff peaks. (Test to see if the sugar is fully dissolved by rubbing a little of the meringue between your thumb and index finger. The meringue should feel smooth, not gritty. If it feels gritty the sugar has not fully dissolved so keep beating until it feels smooth between your fingers). Sprinkle the vinegar and cornstarch over the top of the meringue and, with a rubber spatula, fold in.
Gently spread the meringue inside the circle drawn on the parchment paper, smoothing the edges, making sure the edges of the meringue are slightly higher than the center. (You want a slight well in the center of the meringue to place the whipped cream and fruit.)
Bake for 1 hour 15 minutes or until the outside is dry and takes on a very pale cream color. Turn the oven off, leave the door slightly ajar, and let the meringue cool completely in the oven. (The outside of the meringue will feel firm to the touch, if gently pressed, but as it cools you will get a little cracking and you will see that the inside is soft and marshmallowy.)
Just before serving gently place the meringue onto a serving plate. Whip the cream in your electric mixer, with the whisk attachment, until soft peaks form. Sweeten with the sugar and vanilla and then mound the softly whipped cream into the center of the meringue. Arrange the fruit randomly, or in a decorative pattern, on top of the cream. Serve immediately as this dessert does not hold for more than a few hours.