!To make the Meringues:
Place oven racks in the upper and middle level of your oven. Preheat to 200. Line two baking sheets with parchment paper or silicone baking mats.
Reserving the yolks for the lemon curd, place egg whites into the bowl of your stand mixer fitted with the whisk attachment. Beat on medium speed until foamy. Add the pinch of salt and increase speed to medium-high. Slowly add sugar. Beat until the egg whites become thick and glossy, holding stiff peaks, similar to melted marshmallow.
Fold in the lemon zest and vanilla. Spoon into a piping bag fitted with a large star tip. To make the nest shape onto the parchment, pipe a silver-dollar sized circle, from the center outward, making sure it's solid so it will hold the curd. Then, pipe another layer around the outside edge, leaving a nest in the middle. Repeat until all the meringue has been used.
Bake for 60-75 minutes (you'll need to try one to test doneness- meringue should be crunchy on the outside and no longer sticky, but chewy and airy on the inside. If it's still wet and frothy on the interior, they're not done yet. If it's dry and crispy throughout they are overdone).
Cool completely on racks.
!To make the Curd:
Place a fine mesh strainer over a medium bowl and set aside.
In a medium saucepan, whisk together lemon juice, sugar, eggs, egg yolks, and salt. Turn heat to medium-low and add butter, whisking constantly. Cook the curd until the butter is completely melted and the mixture has thickened significantly, like pudding. It does not need to come to a boil, it will be fully cooked before it comes to a boil.
Pour hot curd directly into strainer, pressing the curd through using a rubber spatula, separating out any egg bits.
Pour curd into a jar and place a piece of plastic wrap directly onto the top of the curd to prevent a thick film from forming. Cover and refrigerate until cold.
Place curd into a piping bag with a small tip or a plastic zip bag with a corner cut off. Squeeze curd slowly into the meringue nests until just full.