Preheat oven to 200 F. Let egg whites stand at room temperature for 30 minutes. Line a baking sheet with parchment paper. Draw a 10-inch circle on the paper. Flip the paper over so circle is on the other side on the pan.
In a small bowl, stir together sugar, cornstarch, and salt; set aside.
For the meringue: In the bowl of a stand mixer fitted with a whisk, beat egg whites on medium speed until soft peaks form. Add the sugar mixture 1 Tablespoon at a time; continue beating on high speed until very stiff and glossy peaks form, about 5 more minutes. Beat in the vinegar and 1/2 teaspoon of the vanilla.
Using a rubber spatula, spread the meringue over the circle. Shape it into a 9″ disk by making the meringue conform to the circular outline; smooth top and sides with rubber spatula.
Bake for 1 hour and do not open the open door (make sure you don’t open to just check on it…it will be fine).
Turn off the oven and let the meringue dry in the oven with the door closed for 30 minutes. Remove from the oven and let it cool completely (about 3-4 hours).
Gently peel parchment paper from the meringue and, using 2 metal spatulas, transfer meringue to a cake stand.
In a medium bowl, beat the whipped cream until stiff peaks form. Pour the whipped cream mixture onto the cooled meringue and spread evenly over meringue’s top using a rubber spatula.
Decorate with mangoes and mango sauce.