Make your crust: Pulse flour and salt in a food processor for a second. Add butter and pulse until butter has been worked through the flour. Add water, 1 tablespoon at a time, until the dough comes together (I used 2 1/2 tablespoons water).
Carefully roll out dough on a lightly floured nonstick surface (like a silicone mat). Roll into a large rectangle. Spray a jelly roll pan (10x15”) with cooking spray. Press into the bottoms and up the sides of your pan. Chill until apples are ready, or cover with plastic wrap and chill for as long as overnight.
Preheat oven to 350°F.
Peel, core, and slice apples to a small dice. Place 1-2 inches of water in the bottom of a pot. Add apples and cook, stirring occasionally, approximately 3-5 minutes after water boils. You want the apples semi-opaque but not mushy.
Mix 1/4 cup sugar and cinnamon in a small bowl and set aside.
Using a hand mixer, mix crumble ingredients in a large bowl. You may need to use your hands or a pastry cutter to break up the large bits of butter.
Once apples are cooked, drain them well. Spread apples evenly over the crust and then sprinkle the apples with the cinnamon sugar.
Sprinkle the crumble over the top of the apples and press to compact.
Bake for 40-50 minutes until topping begins to brown. Cool before cutting. Serve with ice cream or whipped cream.
Store covered in the refrigerator for up to 4 days, or wrap slices with plastic and seal in a ziploc bag, and freeze for up to one month.