Toss the apples with sugar, flour, lemon juice, cinnamon, and nutmeg. Let stand for 15 minutes while the oven heats to 425 F (220 C).
Assemble the Pie:
Fit one crust into the pie plate. Spoon in the apples and their juices, then dot with butter.
Cut the second crust into strips and weave a lattice over the apples. Crimp the edges, brush with egg wash, and sprinkle with coarse sugar. Chill for 20 minutes.
Bake and Cool:
Bake on a lined baking sheet at 425 F (220 C) for 20 minutes. Reduce the heat to 375 F (190 C) and bake for 35 to 40 minutes, until the crust is golden and the filling bubbles.
Cool for at least 2 hours before slicing and serving.