Line a 9x13-inch pan with parchment paper, leaving an overhang for easy removal, and set aside.
In a powerful blender or food processor, blend the Oreos (with cream) until they are crumbs. Reblend any large chunks so the crust will cut nicely. Once all in crumbs, add melted (and slightly cooled) 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.
Scoop the ice cream over the crust in big scoops. Use a 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.
Add the entire jar of hot fudge on top of the ice cream and, using a spatula, spread the fudge into an 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.
Using a spatula, spread the completely thawed whipped topping over the bars into a smooth, even layer. If desired, crush 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.
Let bars stand for 5 minutes at room temperature before cutting and serving. Use the parchment overhang 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.
Notes
Note 1: You can make homemade Cool Whip!
1 cup heavy cream
1/2 cup powdered sugar
1/2 teaspoon vanilla extract
In a stand mixer (with a whisk attachment) add the heavy cream, powdered sugar, and vanilla extract. Beat to combine, then increase the speed and whip until firm peaks form, about 2–4 minutes. With a spatula, spread whipped cream over the ice cream until smooth.Storage: Return any leftovers promptly to the freezer. The whipped topping doesn’t thaw and refreeze very well (it becomes icy) so try to finish the bars a few days after making them.