Line a 9x13-inch baking pan with parchment paper and spray with cooking spray.
Heat butter in a nonstick saucepan over low heat until melted. Add marshmallows and continue cooking, stirring until smooth.
Remove pan from heat before adding cereal and cookies. Stir gently until mixed to avoid breaking up the cookies any further. Then press the mixture evenly into prepared pan.
Cool Oreo rice krispy completely before cutting into bars.
These are my niece Michelle's favorite. I often make them for her whenever she visits.
Cool Oreo rice krispy completely before cutting into bars. 