For the Shortbread Crust:
Mix the butter, sugar, flour and salt in an electric mixer, KitchenAid mixer fitted with the paddle blade. Spread evenly into the base of a 14 x 9 x 1 jelly roll pan (see our recommended pan in Kitchen Essentials). Bake crust in a 350 preheated oven for about 20 minutes or until the edges are light golden brown.
For the Filling:
While the crust is baking, make the filling. Combine the eggs and sugar in an electric mixer, Kitchen Aid stand mixer fitted with the paddle blade. Add the lemon zest, lemon juice and mix, just to combine (over mixing will make the mixture foamy – just incorporate the ingredients until mixed. Add the flour and mix, just to combine - use a rubber spatula to ensure the filling is completely mixed. When the crust is baked, pour the filling directly on top of the crust and bake for an additional 20 minutes, until the center is completely set and lightly golden on the top.
Cool completely before cutting into pieces. Dust with powdered sugar to serve.