Combine all topping ingredients using a fork until completely mixed and crumbly.
Peel, core, and slice apples into thin slices (approximately 1/8 inch). Toss apple slices with sugar, lemon juice, cinnamon, nutmeg and flour.
Layer apple slices in pie shell (it will be really full) and pour any leftover juice over the apples. Top apple slices with topping and pat it down over the apples. Place pie pan on a cookie sheet (they tend to drip over if really full, this will save your oven).
Bake at 450 for 15 minutes, reduce heat to 350 degrees and bake an additional 45-55 minutes. (Poke the center of the pie to make sure the apples are soft all of the way through).
Serve warm or room temperature.
Be sure to keep an eye on your crumble topping. If it starts to brown too early, place a small piece of foil on top to keep it from burning.