Mix flour and salt together in a medium mixing bowl. Cut in butter and shortening using a pastry blender until mixture resembles coarse oatmeal. Stir in ice water until dough comes together into a ball. Divide into 2 pieces.

Preheat the oven to 450 degrees F (230 degrees C).

Transfer dough to a lightly floured surface and roll out into 10-inch crusts. Place 1 crust into a 9-inch pie pan.

Combine blackberries, sugar, and potato starch in a large mixing bowl. Pour the berry mixture into the pie crust. Lay the second crust over the berries. Press edges together to seal; crimp with a fork. Make 4 small slits in the top crust.

Bake in the preheated oven for 15 minutes. Reduce oven temperature to 350 degrees F (175 degrees C). Continue baking until top is golden brown, about 45 minutes.

Let cool completely until set, about 2 hours.