To make the crust: Combine the flour, powdered sugar, salt and butter in a food processor. Pulse until mixture resembles fine crumbs. Press into a lightly greased 11x7-inch or 8 to 9-inch square glass baking dish and bake for 18 to 20 minutes, or until golden brown.
Meanwhile make the filling: Whisk together the sugar and flour in a bowl. Add the eggs, one at a time, whisking well after each addition. Add the zest and lemon juice. Mix until everything is smooth and combined.
Pour filling over hot crust and return to oven to bake for an additional 18 to 20 minutes or until set. When done, the filling will no longer jiggle.
Let cool completely in the pan before slicing and dusting with powdered sugar. For best results refrigerate for an hour or two and serve cold. Store leftovers in the refrigerator.