place oreos in food processor and pulse until ground.

melt marshmallows n butter in microwave until fluffed, about 11/2-2 min.remove from microwave, and add oreos into marshmallows. stir to combine.

transfer to a foil lined 8×8 baking pan.let stand for 10-15 min.remove bars out of pan with edges of foil and cut into squares.