Whisk flour, salt, and sugar. Cut in cold butter until pea‑sized. Add ice water 1 tbsp at a time until dough clumps. Divide, shape into discs, wrap, and chill at least 1 hour.

Roll one dough disc into a 12‑inch circle, fit into a 9‑inch glass pie dish, trim overhang to 1/2 inch. Chill. Roll second disc into another 12‑inch circle.

Toss sliced apples with sugar, flour, cinnamon, nutmeg, salt, and lemon juice until coated.

Pile filling into chilled bottom crust, dot with butter, drape top crust over, trim, fold overhang under, crimp, cut vents, brush with egg wash, and sprinkle with coarse sugar.

Preheat oven with a baking sheet on lower rack at 400°F (200°C). Place pie on hot sheet, bake 20 min. Reduce to 375°F (190°C) and bake 40‑45 min until golden and juices bubble thickly.

Cool on a wire rack at least 4 hours, then slice and serve.