Place cookies in food processor & pulse until they are coarse crumbles

Line an 8x8 inch pan with parchment & give a light spritz with cooking spray

In a large bowl - combine marshmallows & butter

Microwave marshmallows on full power for about 1-1/2 minutes. They should puff up quite a bit.

Remove & immediately mix in the Oreo crumbles until fully mixed in

Transfer to prepared pan & press into an even layer

Top with remaining whole cookies & press in

Allow to cool completely before cutting.

Store in refrigerator in airtight container but bring to room temperature before serving