Preheat your oven to 200°F (93°C) and line baking sheets with parchment paper.

In a mixing bowl, combine egg whites, kosher salt, and cornstarch. Beat on medium speed until frothy, then gradually add sugar and whip until stiff peaks form.

Dollop small mounds of meringue onto baking sheets, leaving space between each.

Bake in the preheated oven for 2 hours until dry and crisp, leaving the door slightly ajar.

While cooling, simmer lemon juice in a saucepan. In a bowl, whisk butter, sugar, and egg yolks. Gradually add lemon juice, then cook over a double boiler until thickened.

Strain the lemon curd through a sieve into a bowl to remove lumps and then chill.

Fill cooled meringues with lemon curd, top with berries and mint, and dust with powdered sugar before serving.