Preheat the oven to 350°F (175°C) and grease a muffin tin.

In a stand mixer, beat room-temperature butter and granulated sugar with fresh lemon zest until light and fluffy.

Add eggs one at a time, followed by vanilla extract and salt, mixing until well combined.

In a separate bowl, whisk together flour, baking powder, and baking soda. Gradually add to wet ingredients, mixing until just combined.

Form 1-inch balls of dough and place them in the prepared muffin tins, pressing down to form cups.

Bake for 7-8 minutes until lightly golden, then cool in the pan for 5 minutes before transferring to a wire rack.

Prepare the lemon curd by blending lemon juice, egg yolks, sugar, cornstarch, and zest in a saucepan over medium heat. Stir until thickened.

Whisk in cold butter once curd is smooth and thick.

Fill each cookie cup with about 1 tablespoon of lemon curd and let cool completely before serving.