Line a 9-inch pie pan with 1 rolled-out crust; trim edges, leaving a ¼-inch overhang. Place in freezer until ready to fill, or at least 20 min.
Heat oven to 425ºF with rack in the bottom third. Cut apples into ¼-inch slices and toss in a large bowl with lemon juice, cinnamon, nutmeg and cornstarch. Add ½ cup Salted Caramel Sauce and toss to combine. Pour apples into chilled pie shell and return to freezer.
Roll remaining crust to a 13-inch circle. Use a paring knife to cut slits or small designs on the top. Brush rim of bottom crust with egg wash and cover with second crust, sealing the edges. Trim edges as necessary to crimp. Brush pie with extra egg wash and sprinkle with crystal sugar; freeze pie again until crust is cold, about 20 min.
Bake pie on a foil-lined baking sheet until crust begins to brown, about 20 min. Reduce heat to 375ºF and bake until crust is golden and juices bubble, 50 to 60 min more. (If crust browns too quickly, tent pie with foil.) Cool pie and serve slices with Salted Caramel Sauce.
Notes
Choose a variety of apples for your pie. Macintosh or Empire are genius for baked desserts. They are sweet and break down to soft bites. But I like to add other apples like Golden Delicious, Pink Lady, and even Granny Smith in for texture and tartness. Play around with your own mix. You can't go wrong with any apples mixed with caramel!