Pulse Oreos in a food processor until fine crumbs are formed. Add the butter and mix until the crumbs are fully coated. Press the crumbs into an ungreased 9×13 in baking dish or pan. Place the pan in the refrigerator while you work on the additional layers.

In a medium bowl, whip the cream cheese until light and fluffy. Add 2 Tbsp. milk and the sugar and mix well. Fold in 2 & 1/2 cups whipped topping. Spread this mixture over the Oreo crust.

In another bowl, combine the pistachio pudding with the 3 & 1/4 cups milk and whisk until pudding starts to thicken. Spread the pudding mixture over the cream cheese layer. Let the dessert rest for about 5 minutes, so the pudding can firm up completely.

Spread the remaining whipped topping over the pudding layer and sprinkle the chopped pistachios on top.

Place in the freezer for 1 hour or let refrigerate for 4 hours before serving.