For the crust: Place the flour, sugar and salt in the bowl of a food processor. Pulse a couple of times to mix. Add the shortening and pulse to combine. Add the butter and pulse until the mixture is coarse and a few pieces of butter are still visible. Add the apple cider vinegar and 4 tablespoons ice water. Pulse to combine. Add more water, 1 tablespoon at a time, until the dough just comes together. Turn the dough out onto a dry surface and divide into into 2 disks, one slightly larger than the other. Wrap in plastic and refrigerate 1 hour or overnight.
Roll the larger disk on a lightly floured surface about 11 inches in diameter and 1/8-inch thick, to fit a 9-inch pie plate. Place in the pie plate, trim to 1/2-inch, and do not crimp the edges. Refrigerator while preparing the filling.
For the filling: Preheat the oven to 400 degrees F. In a medium saucepan over medium heat, combine 1 cup huckleberries with 3/4 cup sugar, orange zest and orange juice. Bring to a simmer and cook until the berries begin to burst and the mixture is saucy, about 5 minutes. Allow to cool slightly. Combine the remaining 5 cups huckleberries with the tapioca in a large bowl. Add the cooked huckleberry mixture to the bowl and gently fold them in.
Pour the filling into the prepared pie shell. Roll the smaller disk of dough on a lightly floured surface to 1/8-inch thick and place on top of the filling. Fold the edges over and decoratively crimp the edges. Cut slits into the top crust to allow steam to escape. Whisk the egg with 1 teaspoon water. Brush the pie with the egg wash and sprinkle with the remaining 2 teaspoons sugar.
Place the pie on a baking sheet and bake for 15 minutes. Reduce the oven temperature to 375 degrees F and continue baking until the crust is golden brown and the filling is thick and bubbly, 50 minutes to an hour. Cool completely before serving. Serve with sweetened whipped cream.
Cook's Note: Fresh berries will hold their shape better than the frozen ones.