In a medium saucepan, whisk together fresh lemon juice, lemon zest, egg yolks, granulated sugar, and salt. Heat over medium-low for 20-25 minutes until it thickens. Stir in cold butter until smooth, then transfer to a bowl and cool.

In a small bowl, whisk together flour, baking powder, and a pinch of salt. In a large bowl, rub together sugar and lemon zest, then cream in softened butter until light. Add egg and vanilla extract, mixing until pale.

Gradually add the dry mixture to the wet ingredients, stirring until just combined. Scoop tablespoon-sized balls, indenting with a measuring spoon. Place on parchment-lined sheet, cover, and refrigerate for about 1 hour.

Preheat oven to 350°F (175°C). Arrange cookie dough on a baking sheet and bake for 8-9 minutes. Cookies should be soft. Remove and refine shapes before cooling on a wire rack.

Dust cookies with powdered sugar. Fill indents with cooled lemon curd. Enjoy!