Preheat the oven to 200°F. Line two baking sheets with parchment paper or silicone baking mats.

In the bowl of an electric mixer, fitted with a whisk attachment, beat the egg whites, salt, and vinegar until they start to foam, about 1 minute. With the mixer running slowly, add the sugar and continue to beat until it forms firm, shiny peaks, about 4-5 minutes. Sift the cornstarch onto the egg whites, add the vanilla, and beat in.

Divide the mixture into 6 equal dollops. With the back of a spoon, create a well in the center of each dollop.

Bake for 1½ hours and then turn off the oven and let cool completely in the oven.

Beat the heavy whipping cream with the powdered sugar until it forms soft peaks. Do not over beat.

Put thawed frozen raspberries and balsamic vinegar (if using) in a blender and blend until smooth. Strain through a sieve.

When the meringues are completely cooled, peel off the parchment paper and place on a plate or serving platter. Spoon or pipe the cream into the meringues. Top with berries, drizzle with raspberry sauce, garnish with mint sprigs, and serve.