Preheat the oven to 450 degree F. For the pastry, stir together 1-1/4 cups all-purpose flour and 1/4 teaspoon salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of mixture; gently toss with a fork. Push moistened dough to side of bowl. Repeat, using 1 tablespoon of water at a time, until flour mixture is moistened. Form dough into a ball on floured surface, roll dough into a 12-inch circle. Ease dough into a 9-inch pie plate. Trim to 1/2-inch beyond edge of plate. fold under extra dough. Crimp edge.
Line the bottom of a pastry-line 9-inch pie plate with a double thickness of foil. Bake in the 450 degree F oven for 5 minutes. Remove the foil and bake for 5 minutes more. Remove the pie shell from the oven and cool slightly. Reduce the oven temperature to 375 degree F.
Meanwhile, in a small bowl stir together the 3/4 to 1 cup sugar, the sour cream, 3 tablespoons flour, and 1/4 teaspoon salt until combined. Set aside.
Place the blackberries in the prebaked pastry shell. Spread the sour cream mixture evenly over the berries.
In a small bowl, stir together the bread crumbs, the 2 tablespoons sugar, and the melted butter or margarine. Sprinkle the bread crumb mixture on the sour cream mixture.
Cover the edge of the pie with foil and bake in the 375 degree F oven for 25 minutes. Remove the foil. Bake for 20 to 25 minutes more or until the top of the pie is golden and the berry mixture bubbles slightly. Makes 8 servings.