Preheat your oven to 325° F and line a 9x13 inch baking dish with parchment paper leaving a 2"overhang on the sides.
In a stand mixer fitted with the paddle attachment, add the butter, confectioners sugar, flour, and salt. Mix on medium speed until a soft ball of dough forms. The dough should come together in one piece and not be sticky.
Press the dough firmly and evenly into the bottom of the prepared pan and bake for 20 minutes. The crust is ready when the middle is firm and the edges are golden brown. Cool for 5 minutes.
Make the filling:
Raise the oven temperature to 350°F. In a medium sized bowl whisk the eggs, juice, zest, sugar and flour until it is combined well and foamy looking.
Pour the filling into the crust and bake for 30 mins.
The bars are done when the edges are golden brown and the top is foamy and slightly firm. The middle should still be a little jiggly.
Cool the bars on the counter for 30 minutes then chill for at least 4 hours or overnight.
Cut and serve cold with dusted confectioners sugar and more zest!
Notes
Using fresh juice is preferred from bottled if you can!To get one cup you will need: