Peel apples and cut them into 1/4-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 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-crust filled pie (unbaked). Crimp edges and refrigerate until ready to use.
Remove crust from refrigerator and scoop cooled filling into crust. With your hands, break apart the crumbs and disperse them over the top of the apples to cover. You may or may not use all of the crumbs (any leftover can be frozen and used for other pies or even coffee cakes).
Place the pie onto a baking sheet lined with parchment and bake at 400° F for 20 minutes. Turn down the temperature to 350° F and continue to bake the pie for another 30 minutes, or until a knife inserted into the pie gives no resistance (cover crust if necessary to avoid over baking).
Serve warm with ice cream or freshly whipped sweetened cream.