In a medium saucepan, combine lemon juice, lemon zest, egg yolks, granulated sugar, and a pinch of salt. Cook over medium-low heat, stirring continuously for about 20-25 minutes until thickened. Remove from heat, whisk in butter, and refrigerate until fully cooled.

Preheat your oven to 350°F (175°C). In a large bowl, whisk together flour, baking powder, and sea salt. In another bowl, cream butter and sugar until fluffy, beat in egg yolk, vanilla extract, and lemon zest, then fold in the dry ingredients.

Portion out the dough into 1-inch balls on a parchment-lined sheet, pressing to form a small indentation. Chill in the refrigerator for 1 hour.

Bake for 9-10 minutes until edges are lightly golden, then cool on the baking sheet.

Fill each indentation with lemon curd, let cool completely, and optionally dust with powdered sugar before serving.