Spray a 9×13 pan with non-stick cooking spray and line the bottom with a layer of graham crackers. (You won't use the entire sleeve of crackers.(
Measure out rice Krispie cereal and set aside. Add 7 cups of mini marshmallows and butter to a large, microwaveable bowl. (I like to spray the bowl and a rubber spatula first with non-stick spray to make this entire process easier!)
Microwave for 1 minute on high, until marshmallows begin to puff up. Remove from microwave and stir in cereal. Once it’s well incorporated, add in remaining mini marshmallows and all but a couple tablespoons chocolate chips. Stir until mixture is combined. Layer Krispies on top of graham crackers and press gently into pan, making the top as level as possible. Sprinkle on remaining chocolate chips.
Cool and cut into squares. (I like to flip the entire pan over onto a cutting board and cut them into squares based on where the graham crackers end. It's just easier this way!)