How to Make It
In a food processor, combine the flour and salt. Add the butter and pulse in 1-second bursts until the mixture resembles coarse meal. Drizzle the ice water over the dough and pulse in 1-second bursts until it just comes together. Turn the dough out onto a work surface, gather any crumbs and pat it into 2 disks. Wrap the disks in plastic and refrigerate until chilled, about 30 minutes.
Preheat the oven to 425°. On a floured work surface, roll out 1 disk of the dough to a 12-inch round, a scant 1/4 inch thick. Ease the dough into a 9- to 10-inch deep-dish glass pie plate. Roll out the second disk of dough to a 12-inch round. Transfer to a wax paper–lined baking sheet and refrigerate.
In a bowl, combine the apples with the sugar, flour, cinnamon, nutmeg and salt. Add the lemon juice and toss well. Let stand for 10 minutes, until the sugar dissolves slightly.
Scrape the apples and any juices into the pie plate and dot with the butter. Cover with the top crust and gently press the edges together. Trim the overhanging dough to about 1 inch and pinch to seal. Fold the dough rim under itself and crimp decoratively. Brush the pie with the beaten egg and sprinkle with the turbinado sugar. Cut 3 small gashes in the top of the pie to vent the steam.
Bake the pie on the lowest shelf of the oven for 30 minutes. Lower the oven temperature to 365° and bake the pie for 45 to 50 minutes longer, until the fruit juices are bubbling through the steam vents and the crust is deeply golden on the top and bottom; cover the pie loosely with foil halfway through baking to keep it from getting too dark. Transfer the pie to a rack and let cool for at least 2 hours before serving.