PREP: Line a 9x13-inch pan with parchment paper, leaving an overhang for easy removal, and set aside.
CRUST: In a powerful blender or food processor, blend the Oreos (don't separate cookie from cream) until they are all crumbs. Make sure to re-blend any large chunks so the crust will cut nicely. Once all in crumbs, add in the melted (and slightly cooled) 7 tablespoons butter. Stir until a thick dough forms and press that mixture into the prepared pan. Use the bottom of a 1-cup measuring cup to press the crust firmly into the bottom of the pan. No need to go up the sides of the pan.
ICE CREAM: Scoop the ice cream over the crust in big scoops. Use a strong silicone spatula to press down the ice cream and smooth it into an even layer. Cover the pan with foil or plastic wrap and freeze for 1-2 hours or until firm.
HOT FUDGE: Add the entire jar of hot fudge on top of the ice cream and, using a spatula, spread the fudge into one even layer. This takes some patience, but it will spread into an even layer. Cover the pan and return to the freezer for 1 hour.
FINISHING: Using a spatula, spread the completely thawed whipped topping over the bars into one smooth and even layer. If desired, crush up the 3-4 extra Oreos (blend or pulse in blender or food processor) and sprinkle the crumbs over the bars. Return to the freezer, covered, to firm up, 20-30 minutes or overnight.
SERVING: Let bars stand for 5 minutes at room temperature before cutting and serving. Use the overhang of parchment paper to pull the bars out of the pan. Use a hot, sharp knife (run it under hot water, dry with a towel) to make cuts into the bars.
STORAGE: Return any leftovers promptly to the freezer. The whipped topping doesn't thaw and re-freeze very well (it becomes icy) so try to finish the bars a few days after making them.
Notes
Note 1: Whipped topping: You can make homemade Cool Whip!
1 cup heavy cream
1/2 cup powdered sugar
1/2 teaspoon vanilla extract
In a mixing bowl attached to a stand mixer (with a whisk attachment) add the 1 cup heavy cream, 1/2 cup powdered sugar, and 1/2 teaspoon vanilla extract. Beat to combine and then increase the speed and whip until firm peaks form, about 2-4 minutes. With a spatula, spread the whipped cream over the ice cream until smooth.