Set out 9 x 13 pan and spray with non-stick cooking spray, or grease with butter.
Add whole Oreos to food processor and pulse until they are fine crumbs. Set aside one cup of the crushed Oreos for the topping.
Mix remaining Oreo crumbs with half a cup of melted butter.
Pat crumb mixture onto the bottom the pan. Push down to make a crust. Place in the refrigerator to chill.
In mixing bowl, mix together cream cheese, 8 ounces of the whipped topping, and one cup powdered sugar.
Spread the mixture over the chilled crust. Place back in the refrigerator to chill again.
Mix instant vanilla pudding and instant chocolate pudding together, adding three cups of cold milk. Whisk until smooth and thick. Refrigerate for several minutes to thicken, if necessary.
Spread pudding mixture on top of the cream cheese/whipped topping layer.
Spread remaining 8 ounces of whipped topping over the third layer. Sprinkle with remaining Oreo crumbs.
Drizzle a light layer of chocolate syrup over the entire cake.
Take chocolate bar, and using a potato or vegetable peeler, peel off slices of chocolate to make curls. Sprinkle chocolate curls on top of layer cake.
Refrigerate until ready to serve.