To make the crust, combine flour, 1¼ teaspoons salt, and butter in a food processor. Pulse in 1-second bursts until the mixture becomes crumbly. Drizzle in ice water and pulse in 1-second bursts until dough begins to stick together. Gather dough and form two disks, one larger than the other. Cover and place in the fridge for 30 minutes, then let rest on counter for 30 minutes.
In an extra-large bowl, mix sugar, cornstarch, cinnamon, nutmeg, and 1/4 teaspoon salt. Peel, core, and thinly slice apples, tossing slices in sugar mixture as you go. Set aside. On a floured surface, roll out the smaller dough and fit to the bottom of a deep-dish pie plate. Stir the apples once more, then begin arranging slices into the pie pan, tightly stacking in layers and doming inward toward the top. Carefully pour ¼ cup of the excess liquid left by the apples into the pie and discard the rest. Roll out second disk of dough and overlap the top of the pie, pressing down lightly to meet the apples. Fold dough edges under, trimming if needed. Cut 8 slits in the shape of a sunburst on top. Whisk egg yolk and dash of water. Brush over the entire crust and sprinkle with coarse sugar (if desired). Place pie in fridge until oven is preheated.
Preheat oven to 425 F. Place pie on a baking sheet with sides and position on bottom rack of oven. Bake 20 minutes, then reduce temperature to 375 F and bake another 40 to 50 minutes, until bubbling and golden brown. If top crust becomes too brown, cover edges or lightly tent with aluminum foil. Let cool before slicing to produce clean edges.
* Mixing 3 or 4 baking apple varieties in a pie builds a blend of flavors and textures.
