In a large mixing bowl, whisk together the 1 cup of whole milk and the instant vanilla pudding mix until smooth. It should thicken within a couple of minutes.
Once the pudding is set, gently fold in the thawed whipped topping using a spatula. Be careful not to deflate the whipped topping; you want to maintain that light, airy texture.
Take about half of the Oreos and crush them into small pieces. You can do this by placing them in a zip-top bag and using a rolling pin or simply pulsing them in a food processor.
Add the crushed Oreos and optional miniature marshmallows to the pudding mixture. Gently fold everything together until well combined.
Transfer the Oreo fluff into your serving dish. Cover it with plastic wrap or a lid and refrigerate for at least 1 hour to allow the flavors to meld and the fluff to set.
Before serving, crush the remaining Oreos and sprinkle them on top of the fluff for an eye-catching presentation. Serve chilled and enjoy every bite!
