Preheat oven to 350 degrees. Liberally spray a 9x13 pan with non-stick spray.
Combine flour, powdered sugar, cornstarch and salt.
Using a pastry blender or your kitchen air paddle attachment, blend in the butter until is resembles coarse crumbs.
Press mixture into the bottom of you pan.
Bake for about 20 minutes or until the edges are golden.
With a hand or stand mixer mix the eggs, sugar, lemon zest, lemon juice and flour until well combined.
Pour over hot crust and return to oven for 18-20 minutes.
Let completely cool on wire rack.
Cut into squares, sprinkle with powdered sugar and refrigerate in a covered container.