1 (16-ounce) package of Oreo cookies
5 cups (1 bag) of large marshmallows
4 tablespoons butter
Line an 8×8-inch baking dish with aluminum foil, allowing the foil to hang over the edges, and set aside.
Place Oreo cookies in food processor (or crush in a large Ziploc bag with a rolling pin) and pulse until crumbly, but not ground.
Melt marshmallows and butter in a large microwave-safe bowl until puffy, about 1 1/2 to 2 minutes. Remove and pour in ground cookies. Quickly stir to combine, then transfer to baking dish.
Allow to set for 10 to 15 minutes. Remove bars from pan by foil edges. Cut, serve, and enjoy!