Mix pastry flour, salt, and sugar. Cut in cold butter until pea-size pieces remain; add ice water gradually until the dough holds when squeezed.
Divide into two discs, wrap, and chill 1 hour. Toss sliced apples with filling sugar, flour, lemon juice, cinnamon, and salt.
Heat the oven to 425°F (220°C). Roll one disc into a 12-inch circle, fit into the pie plate, and refrigerate while rolling the top.
Mound apples and their coating into the lower crust. Add the top crust, trim excess, fold edges together, and crimp firmly.
Cut several steam vents and brush with egg wash. Put the pie on a rimmed baking sheet to catch any drips.
Bake 20 minutes, then reduce heat to 375°F (190°C). Bake 40–50 minutes more, shielding edges if darkening too quickly.
Look for bubbling filling through the center vents and tender apples when pierced. Extend baking if the fruit still resists the tester.
Cool at least 3 hours before slicing so juices thicken. Use a serrated knife for the top crust and a broad server for the filling.
