Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the softened butter and granulated sugar. Beat until light, fluffy, and pale in color, about 3-4 minutes.
Incorporate the vanilla extract and the egg yolk into the creamed mixture. Mix thoroughly until well combined.
In a separate bowl, whisk together the all-purpose flour and fine sea salt. Gradually add this dry mixture to the wet mixture, mixing until just combined.
Carefully fold in the zest of the lemon into the dough.
Using a tablespoon or a cookie scoop, take portions of dough and roll them into balls. Place each ball on the prepared baking sheet, spaced about 2 inches apart.
With your thumb or the back of a rounded measuring teaspoon, gently press down in the center of each cookie to create a small indentation.
Carefully spoon a small amount of lemon curd into each indentation, taking care not to overfill.
Place the baking sheet in the preheated oven and bake for 12-15 minutes until the edges are light golden and the centers remain soft.
Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack. Once cooled, dust the tops with powdered sugar.
Notes
For an appealing display, arrange the cookies on a decorative platter with fresh mint leaves.