Preheat oven to 200 degrees then line a half sheet pan with parchment paper and set aside. Add egg whites to a large glass bowl if using a hand-held mixer, or the bowl of an electric mixer, then let come to room temperature for 30 minutes.
Fit your mixer with the whisk attachment then whip the egg whites on medium-high speed until foamy, 30 seconds. Add salt then continue whipping until soft peaks form (i.e. the egg whites fall over onto themselves after pulling the whisk up) another 30 seconds.
Turn mixer back to medium-high speed then add 1 Tablespoon sugar at a time, whipping for 30-45 seconds before adding the next Tablespoon — don’t rush it! Once all the sugar has been added, scrape down the sides of the bowl then continue whipping until stiff, shiny peaks form and the meringue is smooth when you rub a dollop between your fingertips. If you can still feel a bit of grittiness from the sugar, continue whipping until the meringue is smooth. Add vanilla then whip to combine.
Using two spoons, scoop the meringue into 8 mounds on the prepared baking sheet then use the back of the spoon to make an indentation in the center. The meringues will puff slightly so leave at least 1” between mounds. Bake for 1-1/2 to 2 hours, rotating the pan halfway through, or until the meringues are completely dry on the outside and pull back from the parchment paper without sticking. The meringues should NOT be golden brown, rather they will be a super light champagne color.
Turn the oven OFF then crack the oven door open and let the meringues sit and cool inside for 2 hours. If making a day ahead of time, cool the meringues completely then cover tightly and store at room temperature.
For serving:
Fill the meringue cups with prepared lemon curd then top with fresh berries and serve.