Preheat oven to 350 degrees. Grease a 9 x 13 inch pan and set aside.
For the crust, mix together flour, powdered sugar and salt. Using a pastry blender, cut in the butter until the mixture is crumbly and can be pressed together.
Press the mixture evenly into the greased pan, and bake for 25 minutes until golden brown on the edges.
Meanwhile, whisk together flour and lemon juice until flour is completely dissolved. Then add eggs, sugar, and salt until sugar is completely dissolved.
When the crust is golden, pull it out on the oven rack and pour the lemon/egg mixture over the crust. Decrease the heat to 325 degrees and bake until the filling is springy to the touch, between 25 and 30 minutes.
Cool completely in a refrigerator or freezer. Dust with powdered sugar and cut into 2-inch squares before serving.