Preheat your oven to 350°F (175°C) and prepare a muffin tin by lightly greasing it.

In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy.

Beat in one egg and the vanilla extract until well blended.

In another bowl, whisk together the 2 ½ cups of all-purpose flour, baking powder, and salt.

Gradually add the dry ingredients to the butter mixture, mixing until combined.

Take about 1 tablespoon of dough and press it into the bottom and up the sides of each muffin tin cup. Ensure the dough is even and well-formed.

Bake the cookie cups for 10-12 minutes, or until they are lightly golden. Then, remove them from the oven and let them cool slightly.

While the cookie cups cool, prepare the lemon filling. In a mixing bowl, whisk together 1 cup of granulated sugar and 2 eggs until well combined.

Stir in the lemon zest and lemon juice, then mix in the ¼ cup of flour until smooth.

Once the cookie cups have cooled slightly, fill each cup with the lemon filling until nearly full.

Return the mini lemon bar cookie cups to the oven for an additional 15-20 minutes, until the filling is set and has a slight jiggle.

Remove from the oven and allow them to cool completely in the tin. Once cooled, gently remove the cookie cups and dust them with powdered sugar before serving.