Mash the Oreos in a Ziploc bag

Melt the butter and marshmallows in a sauce pan over medium heat, stirring often

Combine Oreos with Rice Krispies. Mix in melted butter/marshmallow mixture until combined.

Spread into a buttered 9x13 pan. Butter your fingers to press the mixture down evenly into the pan. Let cool completely before you cut and serve.