They hold their shape under heat and their tartness plays against the honey and cinnamon. A sweeter apple will turn to mush and disappear into the crust. Granny Smith holds her own.
If you have a microplane and a whole nutmeg, use it here. A few scrapes is all you need, and freshly grated is noticeably more fragrant than pre-ground — a small thing with a real effect.
Best the day of, but it keeps loosely covered at room temperature for a few hours, or refrigerated overnight. Reheat in a 350°F oven for 8–10 minutes to bring the crust back to life. The microwave will make the pastry sad — the oven is worth it.