Begin by crushing all the Oreo cookies with a food processor (putting them in a ziplock and crushing them with a rolling pin works as well).
Place the Oreo crumbs to a large bowl. Stir in 6 tablespoons of melted butter and use a fork to mix the butter into the cookie crumbs. After the butter is distributed, transfer the mix to a 9 x 13 inch baking dish. Press the crumbs into the bottom of the pan. Place the pan in the refrigerator while you work on the additional layers.
Mix the cream cheese with a mixer until light and fluffy. Add in 2 Tablespoons of milk and sugar, mix well. Stir in 1 and 1/4 cups Cool Whip. Spread the mixture over the crust.
In a bowl, combine chocolate instant pudding with 3 cups of cold milk. Whisk for several minutes until the pudding starts to thicken. Use a spatula to spread the mixture over the previous cream cheese layer. Allow the dessert to rest for about 5 minutes so that the pudding can firm up further.
Spread the remaining Cool Whip over the top. Sprinkle mini chocolate chips evenly over the top. Place in the freezer for 1 hour, or the refrigerator for 4 hours before serving.