Make the Pie Dough by Hand: (see here for instructions for making it in a food processor)

1. In a large bowl, whisk together the flour, cornstarch, and salt. Add the butter and toss to coat it in the flour. Using your fingers, squeeze and work the butter into the flour until the mixture looks shaggy, with a mix of flat pieces and irregular chunks. Some larger pieces can remain, up to about marble size.
2. In a liquid measuring cup, stir the vinegar into the ice water. Drizzle about three-quarters of the liquid over the flour mixture, tossing gently with your fingers to distribute it evenly. Squeeze the dough lightly to check hydration. It should hold together easily when pressed. Add more water, a small drizzle at a time, until the dough comes together, switching to a spatula if needed to moisten any dry pockets.
3. Using your hands, gently bring the dough together into a single pile. Transfer it to a work surface and divide it into two portions, each weighing about 12 ounces. Wrap each portion tightly in plastic wrap and, using a rolling pin, roll the dough out until it stretches to the edges of the plastic wrap. Refrigerate for at least 4 hours, preferably overnight.

Make the Apple Filling:

1. In a large pot, mix together the apples, lemon juice, ⅓ cup (80 grams) of the apple cider, brown sugar, granulated sugar, cinnamon, salt, and nutmeg. Let the mixture sit at room temperature for about 10-15 minutes, until the apples start to release their juices.
2. Cook the apples over medium heat, stirring occasionally, until they begin to soften, about 10 minutes. They should be tender yet still hold their shape, with liquid still visible in the pot.
3. In a small bowl, whisk together the cornstarch and the remaining 2 tablespoons of apple cider to make a slurry. Pour the slurry into the pot and stir to combine. Continue cooking for 2-3 minutes, until the filling thickens and coats the apples. Remove the pot from the heat and stir in the vanilla and butter. Transfer the filling to a shallow container and let it cool completely, preferably overnight

Assemble and Bake the Hand Pies:

1. In a small bowl, whisk together the egg and water to make the egg wash and set aside. Line a 12-by-18-inch sheet pan with parchment paper and set aside.
2. On a lightly floured surface, roll out one disk of pie dough to about a ⅛ inch thickness. Cut out 4-inch circles, rerolling the scraps one time to get additional rounds. Repeat with the second disk to yield about 16 to 18 dough circles.
3. Brush a light layer of egg wash around the edges of one dough circle. Spoon 3 to 4 tablespoons of cooled apple filling into the center, keeping it slightly mounded but away from the edges. Place a second dough circle over the filling and press the edges together to seal, pushing out any air pockets. Crimp the bottom edges up over the top to further seal the pie and add a decorative touch.
4. Once all the pies are assembled, place the hand pies on the sheet pan in the freezer while the oven preheats.
5. Preheat the oven to 400°F and set a rack to the second lowest position.
6. Remove the pies from the freezer, brush the tops with the remaining egg wash, and sprinkle with turbinado sugar. Bake for 30-35 minutes, until the dough is fully baked and lightly golden all over. Transfer to a wire rack to cool, at least 45 minutes.