In a large bowl, whisk together flour, sugar, and salt. Add the cold cubed butter and use a pastry cutter or your fingertips to work it into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
Drizzle in ice water, 1 tablespoon at a time, mixing gently with a fork after each addition. Stop adding water when the dough begins to form large clumps. Test by squeezing a small amount – if it holds together, you're good to go.
Divide the dough into two equal portions and form each into a disc. Wrap each disc tightly in plastic wrap and refrigerate for at least 1 hour, or up to 2 days.
Peel, core, and slice your apples to about ¼-inch thickness. In a large bowl, toss the apple slices with lemon juice to prevent browning.
In a separate bowl, combine sugar, flour, cornstarch, cinnamon, nutmeg, allspice, and salt. Pour this mixture over the apples and toss thoroughly until every slice is coated. Let sit for 15-30 minutes to draw out juices.
Preheat oven to 425°F (220°C).
Remove one disc of dough from the refrigerator. On a lightly floured surface, roll from the center outward until you have a 12-inch circle approximately ⅛-inch thick.
Carefully transfer the dough to a 9-inch pie dish by loosely rolling it around your rolling pin, then unrolling over the dish. Gently press the dough into the bottom and sides without stretching.
Pour the apple filling into the dough-lined pie dish, including any accumulated juices. Dot the filling with the small pieces of butter.
Roll out the second disc of dough and either place it whole on top (cutting vents) or create a lattice pattern. Trim excess dough to 1-inch overhang, fold it under itself, and crimp the edges decoratively.
Brush the top crust with egg wash and sprinkle with coarse sugar if desired.
Place the pie on a baking sheet and bake in the preheated oven for 20 minutes, then reduce temperature to 375°F (190°C) and continue baking for 30-35 minutes until the crust is deeply golden and filling is bubbling.
Allow the pie to cool on a wire rack for at least 3 hours before slicing to let the filling set properly.