#### For the Lemon Curd

1. Combine lemon juice, lemon zest, egg yolks, sugar, and salt in a saucepan. Whisk well.
2. Heat the mixture over medium-low heat for 20-25 minutes until thickened, stirring frequently.
3. Remove from heat, then gradually whisk in cold butter until melted.
4. Transfer to a bowl, cover with plastic wrap touching the surface, and chill completely.

#### For the Lemon Sugar Cookies

1. Whisk flour, baking powder, and salt in a small bowl.
2. Cream butter and sugar until fluffy. Mix in egg yolk, vanilla, and lemon zest.
3. Add dry ingredients and mix until combined.
4. Roll dough into balls, make an indent with a teaspoon, then chill for 1 hour.
5. Preheat oven to 350°F and place chilled dough balls on baking sheets.
6. Bake for 9-10 minutes, then reshape with a cookie cutter if needed.
7. Let cool, then fill each cookie’s center with lemon curd.
8. Optional: Dust with powdered sugar before serving.