Number 1 tip: keep everything as cold as possible. Chill crust ingredients (even the flour!) before starting and keep the peaches/filling as cold as possible right up until going in the oven.
To make the crust, sift together flour, sugar, and salt in a medium bowl. Cut in the shortening with a pastry cutter until the mixture resembles large peas. Whisk together ice water, vinegar, and egg in a small bowl. Add the egg mixture to the flour mixture and stir with a fork until just combined. Divide the dough in half; flatten each half into a disk, and wrap in plastic wrap. Chill for 2 hours, up to overnight.
Preheat oven to 425°F. Line a sheet pan with parchment paper.
Roll out 1 dough disk on a lightly floured surface to form a round, about 1/4-inch thick. Fit the dough into a 9-inch pie pan. Roll out the other dough following the same procedure. Place the second round of dough on the prepared sheet pan. Cut it into 2-1/2 inch-wide strips. Chill the dough while preparing the filling.
Prepare the peaches (see note 1).To make the filling, place the prepared peaches in a large bowl. Add vanilla and 2 tablespoons lemon juice; gently toss to combine. In a separate bowl, stir together the 1/2 cup sugar, cornstarch, and salt. Add to the peaches and gently toss to combine.
Spoon the filling into the dough-lined pie pan. Arrange the pastry strips on the top of the pie in a lattice. Fold the edges under and crimp. Beat the egg and 1 tablespoon water together in a small bowl. Brush the egg wash lightly over the top crust. Sprinkle with the 1 tablespoon sugar. Chill pie for 20 minutes.
Line a sheet pan with aluminum foil and place it on the bottom rack of the oven (to catch any filling that bubbles over). Bake the pie on the center rack for 15 minutes. Reduce oven temperature to 375°F and bake 40–50 minutes more, until golden brown and bubbling, shielding the pie with a sheet of foil after 20 minutes if the crust is getting too brown. Let cool completely on a wire rack, about 2–4 hours, or until thickened and set, before slicing and serving.
Notes
Preparation for unripe peaches: Using a paring knife, score a small “X” in the bottom of the peach, then place the peach in boiling water for about 60 seconds. Using a slotted spoon, remove the peach from the boiling water and place it in a large bowl filled with ice and cold water. As soon as the peach is cool enough to handle, use a paring knife to remove the softened skin (it should slide off pretty easily).Preparation for ripe peaches: Place the peach in boiling water for about 30 seconds. Using a slotted spoon, remove the peach from the boiling water and place it in a large bowl filled with ice and cold water. As soon as the peach is cool enough to handle, gently peel off the softened skin with your fingers (should slide right off). Once the peaches have been peeled, cut in half around the pit and gently twist them to separate the two halves. Remove the pit and slice the peaches into 1/2-inch thick slices.Storage: Store leftover peach pie covered tightly in the fridge for up to 4 days. For longer storage, freeze slices wrapped in plastic wrap and foil for up to 3 months.