Crush 36 regular Oreo cookies into fine crumbs using a food processor, or place the cookies in a large zip-top bag and crush them with a rolling pin.
Transfer the Oreo crumbs to a large bowl. Add 6 tablespoons melted butter and stir until the crumbs are evenly coated.
Press the Oreo mixture firmly into the bottom of a 9×13-inch baking dish. Refrigerate while preparing the next layer.
In a medium bowl, beat 8 ounces softened cream cheese with an electric mixer until smooth and fluffy.
Add 1/4 cup granulated sugar and 2 tablespoons cold milk. Beat until well combined. Gently fold in 1 1/4 cups Cool Whip until smooth.
Spread the cream cheese mixture evenly over the chilled Oreo crust.
In a separate bowl, whisk together two 3.9-ounce boxes of chocolate instant pudding mix and 3 1/4 cups cold milk. Continue whisking for 2 to 3 minutes, until the pudding thickens.
Spread the chocolate pudding evenly over the cream cheese layer. Let the dessert sit for about 5 minutes to allow the pudding to firm up.
Spread the remaining Cool Whip evenly over the pudding layer.
Sprinkle 1 cup mini chocolate chips evenly over the top.
Cover and refrigerate for at least 4 hours, or freeze for 1 hour before serving.
Slice and serve chilled. Cover and refrigerate any leftovers.