Into a mixing bowl, sift the flour, salt, and sugar. Add the shortening and butter and work it in with your hands until the mixture resembles coarse crumbs. Add the water, 1 tablespoon at a time, and work it in with your hands to form a smooth dough. Form into a disk. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
Use as directed in the Baked Sweet Potato Pie recipe.
Yield: dough for 12 (4-inch) pies