Whisk flour, salt, and sugar. Cut in butter until crumbly, then add ice water until dough forms. Chill 30 minutes.

Toss apples with lemon juice, sugars, cinnamon, nutmeg, and flour until coated.

Roll one disc of dough to fit a sheet pan. Add apple filling and dot with butter.

Roll remaining dough and place over filling. Seal edges and cut slits for steam.

Brush with egg wash, sprinkle sugar, and bake at 375°F for 40–45 minutes. Cool before slicing.