Prep Your Battle Station. Preheat your oven to 225°F (107°C) and line a baking sheet with parchment paper. Draw 6-8 circles (about 3-4 inches wide) on the parchment paper, then flip it over so the pencil marks are facing down.
Beat Those Egg Whites. In a clean, dry bowl (seriously, even a tiny drop of grease will ruin everything), beat the egg whites and salt with an electric mixer until soft peaks form. Think of it like whipped cream that's just starting to hold its shape.
Add Sugar Gradually. Now, add the sugar one tablespoon at a time while continuing to beat. Don't rush this part - it's the difference between silky meringue and sad, grainy disappointment. Keep beating until the mixture is glossy and forms stiff peaks. You should be able to hold the bowl upside down without anything falling out (though maybe don't test this over your new rug).
Final Flavor Boost. Gently fold in the vanilla extract, vinegar, and cornstarch. These secret ingredients help create that perfect crispy-outside, chewy-inside texture.
Shape Your Nests. Spoon or pipe the meringue onto your parchment paper circles. Use the back of a spoon to create a well in the center of each nest. Think bird's nest, not pancake.
Bake Low and Slow. Bake for 1 hour to 1 hour 15 minutes. The meringues should be crisp on the outside but not browned. Turn off the oven and leave the meringues inside with the door closed for at least 30 minutes or up to an hour.
The Grand Finale. When you're ready to serve, fill each nest with a generous dollop of lemon curd and top with fresh berries. Dust with powdered sugar and add a mint leaf if you're feeling extra fancy.