On a large piece of parchment paper, using a pie plate as your guide, trace a 10" circle on the paper, flip over and place on a large baking sheet.
Bring to a simmer 1" of water in a saucepan. Place a heatproof bowl over the water- do not let the water touch the bowl. Add sugar and egg whites and beat constantly for 5-6 minutes until the mixtue reaches 160 degrees. Whites will be foamy.
Transfer the mixture to the bowl of a stand mixture and continue beating the whites until stiff glossy peaks form- about 4 minutes. Scrape down the sides and add in the cornstarch, vinegar and vanilla. Beat on high for another 10-15 seconds.
Scoop the meringue onto the parchment lined sheet creating a circle. Using a spatula, build and form a rim or a "crust" along the outside of the circle. The interior depression will later hold the fillings.
Bake the meringue for 1 1/2 hours at 250 degrees. The edges wil be a slightly creamy white color. Do not brown or over cook.
After 1 1/2 hours, turn off the oven leaving the oven door slightly ajar. Allow the meringue cool for about another 1 1/2 hours in the oven. Remove from the oven and let cool for 15 more minutes while you prepare the fillings.
The meringue should lift easily (but handle gently) from the parchment once completely cooled.
Gently place the baked meringue on a large cuting board or on your serving plate to decorate.
You can wrap a baked meringue in plastic and store unfilled at room temperature for up to one week. High humidity affects the texture, so wrap very well if you live in a humid climate.