Make the crust: In a medium bowl, whisk flour, sugar, and salt. Cut in cold butter with a pastry cutter (or fork) until the mixture looks like coarse crumbs with some pea-sized pieces.
Drizzle in 6 tablespoons ice water and stir. Add 1–2 tablespoons more as needed just until the dough holds together when pressed (do not overwork).
Divide dough into 2 discs, wrap tightly in plastic wrap, and chill for at least 30 minutes.
Prep: Preheat oven to 375°F (190°C). Place a baking sheet on a lower rack (or line a sheet pan) to catch drips.
Roll the bottom crust: On a lightly floured surface, roll 1 dough disc into a 12-inch circle. Transfer to a 9-inch pie dish, letting the excess hang over the edges. Chill while you make the filling.
Make filling: In a large bowl, toss sliced apples with granulated sugar, brown sugar, flour, cornstarch, cinnamon, nutmeg, salt, and lemon juice. Let sit 5–10 minutes to get juicy.
Spoon apples (and any juices) into the crust, mounding slightly in the center. Dot with the 2 tablespoons butter.
Top crust: Roll the second dough disc into a 12-inch circle. Lay over the filling (or cut strips for a lattice). Trim to about 1-inch overhang, fold under, and crimp to seal.
Cut 4–6 vents in the top crust. Brush with egg wash and sprinkle with turbinado sugar.
Bake: Bake 50–60 minutes, until the crust is deep golden and the filling is bubbling. If edges brown too fast, cover the rim with foil for the last 15–20 minutes.
Cool: Cool on a rack for at least 2 hours before slicing so the filling sets (cool longer for the cleanest slices).