Heat the oven to 425°F with a rimmed sheet pan on the lower rack.
Toss the peaches with the sugar, tapioca, lemon juice and nutmeg and let them stand for 15 minutes.
Roll one dough disk into a 12-inch circle, fit it in a 9-inch pie plate, spoon in the peaches, and dot with butter.
Cover with the second rolled crust, crimp, cut steam vents, and brush with egg wash.
Bake for 20 minutes, lower the oven to 375°F, and bake 35 to 40 minutes more until the center filling bubbles thickly.
Cool for 3 hours before serving.