In a medium mixing bowl, combine the finely crushed Oreo cookies with the melted butter. Stir until the mixture resembles wet sand.
Press the mixture firmly into the bottom and up the sides of a 9-inch pie dish to form an even crust. Use the back of a spoon or the bottom of a glass to press it down tightly.
Place the crust in the refrigerator while you prepare the filling.
Step 2: Prepare the Filling
In a large mixing bowl, whisk together the whole milk, sweetened condensed milk, cocoa powder, and vanilla extract until smooth and fully combined.
Gently fold in the thawed whipped topping using a spatula until the mixture is light and creamy.
Step 3: Assemble the Pie
Pour the chocolate filling into the chilled Oreo crust, spreading it evenly with a spatula.
Smooth the top and cover the pie with plastic wrap.
Step 4: Chill the Pie
Refrigerate the pie for at least4 hours, or overnight, to allow the filling to set completely.
Step 5: Add Toppings and Serve
Once the pie is set, remove it from the fridge and garnish with your favorite toppings, such as extra crushed Oreos, chocolate shavings, whipped cream, or maraschino cherries.