Line a 9 x 13" baking dish with foil and spray lightly with cooking spray. In a large sauce pan, melt butter over low heat. Still on low heat, add the marshmallows to the melted butter and stir until marshmallows are melted. Remove from heat and stir in Rice Krispies and chopped Nutter Butter cookies. When combined, pour mixture into prepared pan and press evenly. Allow to cool, about 20 - 30 minutes and then cut into squares. DELISH!!!