How to Make It
In a large bowl, whisk the flour, sugar and salt. Add the shortening and, using a pastry blender or 2 knives, cut it into the flour until the mixture resembles coarse meal. Add the ice water and stir with a fork until the dough is moistened. Turn the dough out onto a lightly floured work surface and gather it into a ball. Knead the dough 2 or 3 times, just until it comes together. Divide in half; flatten each piece into a disk. Wrap each disk in plastic and refrigerate until chilled, at least 1 hour.
Preheat the oven to 375°. Let the dough stand at room temperature for 10 minutes. Working on a lightly floured surface, roll out one disk of dough to a 12-inch round. Transfer to a 9-inch glass pie plate. Roll out the remaining dough to an 11-inch round.
Meanwhile, in a bowl, stir the blackberries with the sugar, flour and lemon juice, lightly mashing a few berries; scrape into the prepared pie crust and sprinkle the butter cubes on top.
Brush the overhanging pastry with water and carefully set the top crust over the berry filling. Press the edges of the dough together and trim the overhang to 1 inch. Fold the edge under itself and crimp decoratively. Cut 4 slits in the top crust.
Bake the pie in the center of the oven for 1 hour and 15 minutes, until the bottom crust is golden and the fruit is bubbling. If necessary, cover the edge with foil for the last few minutes of baking. Let the pie cool for at least 4 hours before serving.