Lightly spray a 9 by 9 baking dish with cooking spray (see note). Mix together the Oreos and the melted butter and press into the bottom of the pan.
Beat together the 8 ounces cream cheese, the 4 ounces whipped topping, and the 1 teaspoon vanilla extract. Stir in 1/2 cup of mini chocolate chips. Spread over the Oreo layer.
Beat together the 1/2 cup butter, and 3/4 cup brown sugar until light and fluffy. Beat in the vanilla extract, the salt, 3/4 cup all purpose flour, and 1 tablespoon milk. Stir in the 1/2 cup mini chocolate chips. Gently spread over the cream cheese layer.
Mix together the pudding mix and the 1 1/2 cups milk. Let sit for a few minutes before gently spreading over the cookie dough layer.
Finally, top with 4 ounces whipped topping and then the remaining 1/4 cup mini chocolate chips. Leftovers can be stored in the refrigerator for up to four days.
I really don't think this dish will work in a pan that is bigger than 9 by 9. The layers will be too thin to spread. Though it might work in a pan that is 8 by 8.