Whisk flour and salt. Cut in cold butter until pea-sized pieces remain. Add ice water a tablespoon at a time until dough holds together. Divide into two discs, wrap, and chill 30 minutes.

Toss sliced apples with sugar, cornstarch, lemon juice, cinnamon, and nutmeg. Let sit 10 minutes.

Roll larger disc to a 12-inch circle and line a 9-inch pie plate. Fill with apples. Roll smaller disc for top crust or lattice, trim and crimp edges, cut steam vents. Brush with egg wash and sprinkle coarse sugar.

Preheat oven to 400°F with a baking sheet on the lower rack. Bake pie 20 minutes at 400°F, then reduce heat to 375°F and bake 35 to 40 minutes more until golden and bubbling.

Cool completely on a wire rack, at least 2 hours. Slice and serve.