Preheat oven to 350°. Line a 9x13” pan with foil and spray with cooking spray.
Make the crust: add butter, flour, salt, and sugar to a large bowl. Mix with a hand mixer until it becomes crumbly. (You may need to use your fingers to break up any larger chunks of butter.) Press into the bottom of the prepared pan. Bake for 15 minutes.
While the crust is baking, mix the crumble. Place all the crumble ingredients in the same bowl you used for the crust and mix with your mixer until crumbly.
Again, you may need to use your hands to work in the larger chunks of butter.
After 15 minutes, remove crust from the oven. Spread the cherry pie filling over the crust in an even layer. Sprinkle with mini chocolate chips. Sprinkle the crumble evenly over the filling and press gently to compact. Bake for an additional 20-25 minutes, until topping starts to turn golden.
Cool completely before removing from pan. Cut into squares. Serve alone, or with whipped cream or ice cream. Store in an airtight container in the refrigerator for up to 3 days.