Prepare the crust: in a medium bowl, mix together all-purpose flour, powdered sugar, and a pinch of salt. Add the melted unsalted butter and stir until a soft dough forms.
Press the dough evenly into the prepared pan, ensuring a smooth layer. Bake for 25-30 minutes until the crust is lightly golden around the edges.
Pour the lemon filling over the warm crust. Bake the pan for 20 to 25 minutes until the filling is set and firm in the center.