Preheat your oven to 200°F (90°C). In a clean mixing bowl, whisk the room-temperature egg whites and kosher salt until foamy. Gradually add granulated sugar, beating until stiff peaks form (about 5 minutes). Gently fold in cornstarch, white wine vinegar, and vanilla extract.

Line a baking sheet with parchment paper. Dollop or pipe small meringue rounds onto the parchment, about 1–2 inches in diameter.

Bake for 2 hours until the meringues are completely dry and crisp. Turn off the oven and cool inside until room temperature.

In a saucepan, combine lemon juice and zest. Cook over medium heat until slightly reduced. In a separate bowl, cream together unsalted butter and sugar until fluffy, then add egg yolks and whole eggs along with salt.

Pour the butter and sugar mixture into the saucepan, stirring constantly over low heat. Cook for about 10 minutes, whisking until thickened and coats the back of a spoon.

Strain the lemon curd through a fine sieve into a bowl to remove any lumps. Allow cooling slightly before transferring to an airtight container; refrigerate for at least 30 minutes.

Fill the center of each meringue shell with a spoonful of chilled lemon curd. Top with fresh berries and dust with powdered sugar for presentation.

Garnish each meringue with a sprig of fresh mint before serving.