Peel apples and cut them into ¼-inch thick slices. Place in a large (4 qt) saucepan and add sugar, cinnamon, nutmeg, and butter over apples and mix well. Heat over medium heat, stirring frequently, until apples release their own juices and are reduced by about ⅓. Turn heat off and add tapioca starch. Stir well and set aside to cool completely. For quicker cooling, spread filling out on a baking sheet.
FOR THE CRUMBLE:
Mix all ingredients with a fork (or your hands) until well blended. It should resemble a firm cookie dough. Chill for at least 30 minutes.
FOR THE CRUST:
Proceed with crust per instructions in recipe for one parbaked pie crust.
TO ASSEMBLE:
Scoop cooled apple filling into parbaked crust. With your hands, break apart the crumbs and disperse all but about 1 cup of them over the top of the apples to cover.
Place the pie onto a baking sheet lined with parchment and bake at 425° F for 20 minutes. Turn down the temperature to 350° F and continue to bake the pie for another 10 minutes. Remove the pie from the oven and add the rest of the reserved crumb topping (on top of the precooked crumbs). Shield the crust if necessary and return the pie to the oven and bake for an additional 40-50 minutes, or until a knife inserted into the center goes in with no resistance. (If you're using a regular pie pan and not a deep dish, you will need to reduce the baking times).
Remove from the oven and let cool completely (or be a risk taker and cut while still warm. It'll ooze everywhere, but it'll be so good with a big scoop of vanilla ice cream on top that no one will care how messy it looks). 😋😋😋
Notes
Whole pie can be frozen prior to baking, well wrapped, for up to 3 months. Add all of crumb mixture on top before freezing. Proceed with baking instructions, avoiding removing pie to add additional crumbs, and adding about 30 minutes onto bake time at the end. Baked pie will keep at room temperature or in the refrigerator for up to 5 days.