Preheat oven to 325˚F. Line 2 baking sheets with a silicone mats or parchment paper.
In a mixer, beat butter and sugar together fitted with a paddle attachment until creamy, about 1 to 2 minutes. Add vanilla and beat until combined.
Beat in flour and salt, mixing until just combined.
Roll 1 1/2 Tbsp of dough into a dough ball. Place dough balls 1 inch apart on prepared baking sheets. Press down the center of each ball with a spoon, forming a small indent. Fill each with lemon curd.
Bake 15-20 minutes or until golden brown on the bottoms. Transfer cookies immediately to a cool, flat surface to cool to room temperature.
Increase oven temperature to 350˚F.
Add egg whites and sugar for the meringue topping in the clean bowl of a mixer fitted with the whisk attachment. Whisk on medium-high speed until stiff peaks form. Dollop or pipe the meringue on top of the cooled cookies.
Bake for an additional 5 to 8 minutes, until the meringue begins to brown*. Cool for 5 minutes before serving.
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notes
*If the tops aren't browning as much as you would like, you can brown them more under the broiler (keep a close eye on them so they don't burn!) or with a kitchen torch.