Set the ice cream out on the counter to soften while preparing the Oreo crust.
Take a large zip-lock bag and place all the Oreo cookies inside. Seal the bag shut and place it on the counter. Using a rolling pin, crush the cookies until they are small chunks/crumbs. You want them still to be chunky and small, but not fine crumbs.
Set aside 1/3 of the cookie crumbs for the topping.
Pour remaining cookie crumbs into a 9×13-inch baking pan. Pour the melted butter over the crumbs and mix well to combine. Once combined, press into the bottom of the pan to form a crust.
In a large mixing bowl, add the softened vanilla ice cream and thawed Cool Whip. Whisk or stir together until combined.
Add the instant pistachio pudding mix to the ice cream mixture. Whisk until well combined.
Spread evenly all over the Oreo cookie crust. Sprinkle the reserved Oreo crumbs evenly over the top, pressing down lightly. Cover and freeze for at least 6 hours or overnight.
Remove from the freezer 20 minutes before cutting into squares. Top with hot fudge and whipped cream, if desired. Serve and enjoy!