Preheat oven to 350F. Grease a 9x13-inch metal baking pan. Set aside.
To make the crust, add the flour and salt to a large mixing bowl.
Stir to combine.
Add butter, and cut in until mixture forms crumbs.
Add the crumbs to the prepared baking pan.
Press into the bottom of the pan.
Bake about 20 minutes, or until the edges are just beginning to lightly brown.
Set aside to cool while you prepare the filling and topping.
To make the filling, add the apple slices, sugar, and apple pie spice to a large mixing bowl.
Toss to combine.
Spoon the apple slice mixture over the crust.
To make the topping, add the flour, sugar, and butter to a medium mixing bowl.
Cut butter in until mixture forms coarse crumbs.
Sprinkle the topping over the apples.
Bake for about 50-65 minutes, or until the apples are soft and the topping is golden brown.
Cool in the pan before cutting and serving.
Notes
Butter: I use salted butter in this recipe.
Apples: I like to use a combination of baking apples for this recipe. Apples like Granny Smith, Pink Lady, and Honeycrisp work well. Also, I slice my apples about 1/8-inch thick.
Crust: You may find that you need to add a little bit of ice water to the crust to get it to the right consistency.
Baking: To keep the topping from overbrowning, you can start checking it around 35 minutes in. If it starts to brown too quickly, simply tent a piece of aluminum foil over the top.