1) To make the crust: In a medium bowl, whisk together the flour and salt.
2) Add the shortening, mixing till well combined.
3) Cut the butter into small cubes or pats, and work it into the dry ingredients (using your fingers, a pastry blender or fork, or a mixer) until the dough is unevenly crumbly.
4) Sprinkle in the ice water, continuing to mix until the dough is cohesive. Grab a handful; if it holds together willingly, and doesn't seem at all dry or crumbly, you've added enough liquid.
5) Divide the dough roughly in half, with one half slightly larger than the other. If you have a scale, the pieces will weigh about 11 ounces and 9 ounces.
6) Shape each piece of dough into a disk. Roll the edges along a floured work surface (as though the disk were a wheel), in order to smooth them out.
7) Pat each disk till it's about 1" thick, wrap in plastic wrap, and refrigerate for a minimum of 30 minutes. You may also chill the dough overnight, or for up to 3 days.
8) Remove the dough from the refrigerator. If it's been chilled longer than 30 minutes, allow it to warm a bit and become flexible, about 15 to 30 minutes. While the dough is warming, prepare the filling, and preheat the oven to 350°F.
9) To make the filling: Place the sliced apples in a medium mixing bowl, and stir in the sugar, boiled cider, spices, salt, vanilla, and lemon juice. As you stir, the mixture will become syrupy.
10) Add the butter and Pie Filling Enhancer or flour, and stir until everything is well blended. Set it aside.
11) Flour your work surface, and roll one piece of the dough into a 14" circle. Transfer the dough to a 9" regular (not deep-dish) pie pan that's at least 1 1/4" deep.
12) Spoon the filling into the crust.
13) Roll the top crust about into an 11" circle, and place it over the filling.
14) Fold the edge of the bottom crust up over the edge of the top crust, squeeze them together, and crimp nicely. Cut a decorative slit (or a quarter-sized hole) in the center of the crust, for steam to escape.
15) Place the pie pan on a cookie sheet (to catch any spills), and bake the pie for 45 minutes.
16) Gently place a sheet of aluminum foil atop the pie, covering its entire surface, and continue to bake for an additional 1 hour, 15 minutes, for a total of 2 hours, till the top crust is golden brown and the filling is bubbly.
17) Remove the pie from the oven, and allow it to cool overnight, for best texture. If you cut into it too soon, the filling will be watery, and will ooze out.
18) To serve warm, heat individual slices briefly in the microwave. Serve with vanilla ice cream, if desired.