6 tablespoons cold unsalted butter, cut into 1/2-inch dice
1/2 cup ice water
In a food processor, pulse the flour with the sugar and salt until combined. Add the shortening and butter and pulse until the mixture resembles small peas. Sprinkle the water on top and pulse just until the dough comes together.
Turn the dough out onto a lightly floured surface and knead 2 or 3 times. Divide the dough in half and pat into disks. Wrap in plastic and refrigerate until firm, at least 30 minutes.
Preheat the oven to 350°. Let the dough stand at room temperature for 10 minutes. On a lightly floured surface, roll out 1 disk to a 14-inch round 1/8 inch thick. Wrap the pastry around the rolling pin and carefully fit it into a 10-inch glass pie plate. Trim the overhang to 1/2 inch. Fold the overhang under and crimp the edges. Refrigerate the uncooked pie shell for 10 minutes. Repeat with the remaining pie dough.
Line the pie shells with foil and fill with pie weights or dried beans. Bake in the center of the oven for 20 minutes, or until just set. Carefully remove the foil and weights and bake the pie shells for 10 minutes longer, or until lightly browned and cooked through. Let cool completely before filling.
The pie shells can be kept wrapped in plastic at room temperature for up to 2 days. Alternatively, the dough disks can be frozen for up to 1 month.