Chowhounds have good tips for handling the apples in your apple pie. greygarious tested dozens of varieties of apple for pie, and her favorites are Empire, Northern Spy, and Macoun. She also likes to use a mixture of Macintosh and Honeycrisp. heypielady favors Northern Spies as well, but also recommends Cortlands as an easy-to-find alternative.
roxlet slices her apples very thinly with a mandoline. She finds they pack into the pie shell well, leaving very few gaps, and when the pie is baked, there’s no pocket between the apples and the top crust.
greygarious recommends a rotary apple peeler, corer, and slicer if you bake a lot of pies. This gadget does all those tasks at once, and produces a spiral-cut apple that’s easy to break into flat crescents, which neatly fill the pan with virtually no gaps.
TrishUntrapped recommends microwaving sliced hard apples briefly to par-cook, to ensure they cook through when you bake your pie.
Board Link: Apple Pie: Cutting up the apple, preferences?