Beat egg whites, cream of tartar and salt until soft peaks form. Continue beating while gradually adding sugar and cornstarch.
Once meringue is glossy, and stiff peaks form fold in vanilla.
On a parchment lined baking sheet, spread the meringue into 8-10" round mounds. Build up sides, leaving a slight depression in the center for the filling (like a pizza).
Place baking sheet in the oven, and immediately reduce oven temperature to 250°F. Bake for 50-60 minutes, or until the meringue is crisp to the touch on the outside, and white (not tan-colored or cracked).
The interiors should have a marshmallow-like consistency.
If they appear to be taking on color or cracking, reduce temperature 25°F, and rotate pan .
Gently lift from the baking sheet and cool on a wire rack.
Once cool, keep in an air tight container until ready to fill and serve.
To serve, whip cream with sugar and spread over meringue. Top with fresh fruit.