Place the cookies in a freezer bag and crush until they are broken down to small-medium sizes.

Set a pan to medium heat and melt the butter. Add the marshmallows and mix until completely melted. Remove the pan from the heat and add the Oreo cookies, folding until fully combined.

Spray a 9x9 inch baking pan with cooking spray and pour the mixture into the pan. Grease your hands and press it into the pan. Place in the fridge until firm, about 30 minutes.

Slice into bite-sized pieces and enjoy!