In a large bowl, use a pastry cutter to gradually work the shortening into the flour until it resembles coarse meal, 3 to 4 minutes. In a small bowl, beat the egg with a fork and pour it into the flour mixture. Add the ice water, vinegar, and salt. Stir together gently until all of the ingredients are incorporated and the dough sticks together when pinched.

Divide the dough into 2 equal pieces. Form them into balls, then place each ball in a 1-gallon zip-top plastic bag (do not seal). Using a rolling pin, slightly flatten each ball of dough into a disk (about ½ inch thick) to make rolling easier later. Seal the bags and place them in the freezer until you need them. (If you will be using the dough immediately, it’s still a good idea to place it in the freezer for 25 to 30 minutes to chill.)

When you are ready to use the dough to make a crust, remove from the freezer. On a generously floured surface, roll the dough, starting at the center and working your way out. (Sprinkle some flour over the top of the dough if it’s a bit too moist.) Be gentle and patient; it'll take a little time to get the dough completely rolled out. If the dough is sticking to the countertop, use a metal spatula and carefully scrape it up, flip it over, and continue rolling and adding more flour to the surface and dough as needed until the dough is approximately 2 inches larger than your pie plate.

Using a spatula, carefully lift the dough from the surface of the counter into the pie plate (or you can roll the pastry over the rolling pin, lift it onto the pie plate, and unroll it). Lift the edges of the dough gently and allow the dough to settle naturally into the plate, fitting snugly along the bottom and sides without pressing or stretching (to avoid shrinking during baking). Trim any excess dough, leaving an overhang of about 1 inch. Go around the pie plate, pinching and tucking the dough under itself to create a clean edge.

If you are making a single-crust pie, crimp or flute the edges as desired, using a fork or your fingers. The crust is now ready to be par-baked or filled, as your recipe specifies. If you are making a double-crust pie, roll out the remaining dough and use it to top your filling.