Preheat oven to 350°.
Line a 9 x 13 pan with parchment paper. Get food processor ready with the metal blade.
Crust:
Place the flour and powdered sugar in the food processor and pulse til mixed. Add the chilled butter , toss the cubes to coat with the flour mixture, then pulse everything together in a food processor until it's light yellow, dry, and sandy. (if you overmix, then it becomes a dough).
Empty the crust mixture into the lined pan. Shake the pan lightly to spread it out evenly, then pat down firmly. Remove from oven when it's light golden in color (depends on your oven as to the length of time I invariably bake it longer than 20 min).
While the crust is baking away, start preparing the topping. Thoroughly clean the food processor bowl and blade again, because you'll be using it to make the topping.
Topping:
Take the sugar and lemon zest and process them until you dont see any visible lemon zest. Then add the other dry ingredients and pulse together til thoroughly mixed. Add the eggs and lemon juice til thoroughly mixed. I usually use around ½ C of freshly squeezed lemon juice and the zest from how ever many lemons it takes to make ½ C of the juice. (This could be anywhere from 2 4 lemons depending on size). Pour over the already baked crust, and place back in the oven.
Bake until lightly golden, and the filling is set (doesnt jiggle for my oven, it takes longer than 25 min). Let it cool down completely, then lift it entirely out of the pan using the parchment paper. I use a long slicing knife to cut this into small pieces (wiping the blade well between cuts). Lastly, dust with powdered sugar. If need be, you can place the cut pieces back into the pan still on the parchment paper (for ease of transport).