1. Preheat Oven: Preheat your oven to 375°F (190°C) and spray a mini muffin tin with nonstick cooking spray.
2. Prepare Dry Ingredients: In a small mixing bowl, mix together the flour, baking soda, and baking powder. Set aside.
3. Cream Butter and Sugar: In a large mixing bowl, cream the softened butter and sugar together until fluffy. Beat in the egg and vanilla until well combined.
4. Combine Ingredients: Gradually add the dry ingredients to the wet mixture, mixing until fully combined.
5. Form Cookie Cups: Roll 1-inch balls of dough and place them in the muffin tin. Bake for 8-10 minutes, or until golden brown.
6. Create a Cup Shape: Once baked, press down the center of each cookie to form a cup and allow them to cool completely in the tin.
7. Make Lemon Curd Filling: In a separate bowl, cream the softened butter and sugar together. Mix in 2 whole eggs, 2 egg yolks, and the lemon juice. Cook the filling over medium heat, whisking continuously until it thickens, about 5 minutes. Let it cool slightly.
8. Fill Cookie Cups: Spoon the lemon curd filling into each cookie cup. Top with lemon zest and chill until set.
9. Serve: Remove the cookie cups from the tin, sprinkle with powdered sugar, and serve.

Prep Time: 40 minutes | Cooking Time: 15 minutes | Total Time: 55 minutes
Calories: 235 kcal | Servings: 24 servings