Line an 8×8 glass baking dish with foil or parchment & set aside. ( I typically would use parchment but in this recipe, I prefer the foil instead)
Place your Oreos in food processor & pulse until you have thick crumbs. (the whole Oreo- do not take out the creamy center)
In a large bowl – combine your butter & marshmallows.
Place in microwave & cook on high 1-2 minutes. Marshmallows will puff up significantly but they need to be melted enough that they will mix when stirred.
Once melted enough- pour in your ground Oreos & start mixing until completely combined & there are no more loose crumbs at the bottom of the bowl.
Transfer to your prepared dish & press in to flatten & fill in the dish.
Sprinkle your rough chopped peppermint candy bar on top – it will get a little melted from the warmth of the bars- that’s perfect.
Cover & allow to sit at room temperature 2 hours before serving. OR you can pop in the refrigerator for about 20 minutes & then let come back to close to room temp before cutting.