
Preheat oven to 350ºF. Spray an 8x8-inch baking dish with cooking spray or line it with parchment paper. Set aside.
Place all of the crust ingredients into a large bowl. Use a spatula (or your hands) and stir together until a crumbly mixture forms that can hold its form.
Transfer the crust mixture into the prepared baking dish. Use a spatula to flatten the crust mixture evenly into the pan. The more tightly packed the mixture, the better.
Bake until golden brown, about 15-17 minutes. Keep the oven on while you make the filling.
While the crust is baking, make the apple filling. Begin by cooking down the apples. Placing all of the filling ingredients into a medium-size pot set over high heat. Bring the mixture to a boil.
Once boiling, reduce heat to low and simmer until the filling has reduced and thickened, about 7-9 minutes.* Stir every so often.
Remove the pot from the heat. Use a fork to mash the apples so that the filling is a combination of apple mash and apple chunks.
Pour the apple filling over the baked crust. Use a spatula to evenly spread it out. Set aside.
Place all of the ingredients for the crumble topping into a medium bowl. Use a fork (or pastry blender) to cut in the ingredients until a crumble forms.
Evenly sprinkle the crumble topping on top of the apple filling.
Bake until the crumble topping is golden brown, about 26-28 minutes.
Remove from the oven and let cool for 10-15 minutes. Transfer the bars to the refrigerator and chill for at least an hour before slicing and serving.