Prepare the crust. In a medium bowl, whisk together gluten-free flour, raw cane sugar, xanthan gum, and salt. Add butter to the flour mixture and work it with a pastry cutter until the butter reduces to pea size pieces. Mix vinegar with iced water and add little by little to the flour mixture. Continue working the dough with your fingers. You may not need all the water. The dough is ready when you pinch it with your fingers and it holds together. The dough will look crumbly. Empty the dough mixture into a flat surface and use your hand to knead just enough to form a disk. Do not over knead. The secret to a flaky pie crust is to touch it as little as possible. Wrap disk in plastic paper and place in the refrigerator for at least one hour.

Prepare the crumble topping. Combine almond flour, walnuts, raw cane sugar, oats, salt, and cinnamon in a small bowl and stir together. Add the butter to the mixture and using your fingers, combine the butter with the dry ingredients until small clumps form. Place in the refrigerator until ready to use.

Prepare the filling. In large Ziploc bag, combine all the dry ingredients except the cornstarch. Peel, core, and slice the apples into ½-inch wedges. Add apples to sugar mixture and combine making sure all apple slices are covered with the mixture. Allow to rest in the refrigerator while the pie crust is ready to roll, about one hour.

Preheat oven to 350°F. Remove pie dough from the refrigerator. Allow the dough to rest for about 5 minutes at room temperature to allow easier rolling. 

Roll out the dough with a rolling pin on a lightly floured surface to a 10-inch circle. Place onto a 9-inch pie plate. Gently press the pie dough edges to create a nice pattern.

Add cornstarch to apples and mix well inside the bag. Make sure the cornstarch is dissolved and distributed all over the apples. Pour the apple mixture into the pie shell and arrange the apples to fill any gaps. Add all the juices in the bag on top of the apples. Distribute the crumble topping evenly on top of the apples and press gently.

Place the pie on a baking sheet and bake for 1 hour and 30 minutes or until the crust and top of the pie are golden brown. If the crumble is browning too quickly, cover with a piece of aluminum foil. Remove from oven and allow pie to cool down before cutting.