Have a 19-inch Oreo crust ready in a pie plate (store-bought or homemade) and set aside.

In a large bowl, whisk the 13.4 ounce box instant vanilla pudding mix with 1 ½ cups (355 ml) nonfat milk until smooth. Let the mixture sit about 3–4 minutes, or until it reaches a soft-set consistency.

Add the entire 18-ounce container of Cool Whip to the pudding. Gently fold with a rubber spatula until the mixture is uniformly combined.

Stir in the 30 chopped Oreos and 2 cups mini marshmallows until evenly distributed through the filling. (If your Oreos are not yet chopped, chop them before adding.)

Spoon the filling into the prepared 19-inch Oreo crust, spreading evenly and piling slightly higher than the rim if needed. If you have extra filling, transfer it to a covered container and refrigerate.

Cover the pie and chill in the refrigerator for at least 4 hours before serving. Store the assembled pie in the refrigerator for up to 3 days.