Combine the flour and salt in a mixing bowl. Cut in shortening with pastry blender until small pea-size pieces. Toss in cold water, one tablespoon at a time, with fork until the dough is sticky enough to hold together. Roll out dough, press into a 9-inch pie plate and crimp the edges. Bake the crust at 400ºF for 7 minutes.
For the filling:
Separate egg yolks from whites. Set whites aside for another recipe. Zest and juice the lemons. Pour the water into a medium-sized sauce pan. When it comes to a boil, mix in juice, sugar, cornstarch, and well-beaten egg yolks. Stir until well blended and cook until thick; stirring constantly. Remove from heat, quickly stir in 1 tablespoon butter until melted. Pour into the baked crust.
For the topping:
Toss the flour, lemon cookies, brown sugar and butter in a food processor and pulse for a few seconds, until it’s crumbly but not too fine. Pour over the filling, bake at 350ºF for 17-20 minutes, or until the topping is slightly brown and all the butter has melted. Cool.