Preheat your oven to 350°F (175°C). Grease an 8x8-inch baking dish.
In a medium bowl, mix together the sifted flour, room temperature butter, and powdered sugar until crumbly. Press into your prepared baking dish.
Bake for 15 minutes or until lightly golden. Set aside to cool.
In another bowl, whisk together the granulated sugar, 2 tablespoons of flour, limoncello, beaten eggs, lemon juice, and lemon zest.
Pour the lemon mixture over the baked crust and return to the oven.
Bake for an additional 15 minutes, or until the filling is set. Allow to cool completely before cutting into bars.