Add 1 cup cold cubed unsalted butter and 1/2 cup cold cubed shortening (if using) to the flour. Use a pastry cutter, two forks, or pulse in the food processor until mixture resembles coarse meal with pea-sized butter pieces remaining (about 8–12 pulses).

Add liquid

Combine 6 tablespoons ice water and 1 teaspoon vinegar (or lemon juice). Sprinkle the liquid over the flour mixture a tablespoon at a time, gently tossing with a fork after each addition until dough just comes together and holds when pressed. You may not need all the water; use just enough for cohesion.

Form and chill

Divide dough into two balls (about a 2:1 ratio for bottom/top if you prefer), flatten each into a disk, wrap in plastic, and chill at least 1 hour (or up to 2 days) to relax gluten and firm the fat.

Roll out

On a lightly floured surface, roll one disk to a 12-inch circle about 1/8 inch thick for the bottom crust. Carefully transfer to a 9-inch pie pan, easing it into the pan without stretching. Refrigerate while you roll the top crust.

Apple filling

Prepare apples

Peel, core, and thinly slice enough apples to measure 6 cups (about 6 medium apples). Place the slices in a large bowl and toss with 1 tablespoon lemon juice to prevent browning.

Mix filling

To the apples add 3/4 cup granulated sugar, 1/4 cup packed light brown sugar, 1 teaspoon ground cinnamon, 1/4 teaspoon ground nutmeg, 1/4 teaspoon fine salt, and 2 tablespoons cornstarch. Toss until apples are evenly coated. Add 1 teaspoon vanilla extract and mix gently.

Assemble filling in crust

Remove the chilled bottom crust from the refrigerator. Mound the apple mixture into the crust, arranging slices so they sit evenly. Dot the apples with the 2 tablespoons of unsalted butter cut into small pieces.

Top crust and finishing

Top crust placement

Roll the second disk of dough to a 12-inch circle (or shape into lattice if desired). Drape it over the apples. Trim both crust edges to about 1/2 inch beyond the pan rim. Fold the top and bottom crust edges together and crimp to seal. Cut 4 small vents in the top if using a full top crust; if lattice, ensure openings for steam.

Egg wash

Whisk 1 large egg with 1 tablespoon milk or cream. Brush the top crust evenly with the egg wash and sprinkle with 1 tablespoon coarse sugar if desired for sparkle and crunch.

Bake

Place the pie on a rimmed baking sheet (to catch any drips). Bake in a preheated oven at 425°F (220°C) for 20 minutes. Without opening the oven, reduce temperature to 375°F (190°C) and continue baking for 35–45 minutes more, until the crust is golden and juices bubble through vents or lattice. If edges brown too quickly, cover with foil or a pie shield after ~25 minutes at the lower temperature.

Rest

Remove pie from oven and cool on a wire rack at least 2 hours (preferably 3) before slicing so the filling sets. Serve warm or at room temperature, plain or with vanilla ice cream.