Preheat oven to 275℉. If desired, trace 6-8 circles onto a piece of parchment paper, flip paper over and lay on baking sheet. Set aside.

Place sugar and cornstarch in a small bowl and whisk together.

Place egg whites in a stand mixer with whisk attachment. Beat for 1-3 minutes, until soft peaks form.

With mixer running on medium-high speed, slowly add sugar mixture, one spoonful at a time until all is incorporated.

Increase speed to high and continue mixing 3-4 minutes longer, until mixture is smooth and glossy and holds stiff peaks.

Add vanilla and vinegar and mix to combine, scraping down edges with spatula.

Place mixture in a piping bag and pipe rounds onto prepared sheet, or spoon mixture onto the rounds and shape with a spoon.

Use a spoon to make a little indentation in the center of each mound.

Place pan in oven and decrease temperature to 250℉. Bake for 45-50 minutes, until edges are set and sound hollow when tapped.

Turn off oven and with oven door cracked open, let pan cool completely.

To fill, whip cream, vanilla, and sugar until soft peaks form. Spoon into center of each shell and then top with desired fruit.