Start by lining a 9x13-inch baking dish with parchment paper. Make sure to leave enough overhang on the sides; this little trick will help you remove your sundae bars afterward without any hassle.

Using a powerful blender or food processor, crush the Oreos into fine crumbs—there’s no need to separate the cream. If you happen to get larger chunks, reblend to ensure that the crust cuts evenly. Once you’ve achieved fine crumbs, transfer them to a mixing bowl.

Pour the melted butter into the bowl of Oreo crumbs. Use a spatula or your hands to mix it until it forms a thick, cohesive dough. This should adhere together nicely but not be overly sticky.

Take the Oreo mixture and firmly press it into the bottom of the prepared baking dish. Use the bottom of a measuring cup to ensure it’s compact, but there's no need to shape it up the sides. The crust should be even and flat.

Scoop the cookies and cream ice cream in large dollops over the pressed Oreo crust. A lot of folks use a silicone spatula to spread the ice cream into an even layer. Don’t be afraid to really smooth it out! Once done, cover the pan tightly with foil or plastic wrap and place it in the freezer for 1 to 2 hours to firm up.

After the ice cream is firm, drizzle the hot fudge sauce all around the top. As you spread it, take your time. Patience pays off, and you want it as even as possible for optimal layers of flavor. Cover the pan again and return it to the freezer for another hour.

With the fudge layer set, it's time to gently add the entirely thawed whipped topping over the fudge. Again, take your time to make it smooth and even. For an extra touch, crush 3-4 additional Oreos in a blender and sprinkle them over the top.

Cover the pan once more and return it to the freezer for at least 20 to 30 minutes, or overnight if you can wait! This allows the sundae to set thoroughly.

Before serving, let the sundae bars sit at room temperature for about 5 minutes. The warm edges will make cutting easier. Use the parchment overhang to pull the sundae out of the dish. Grab a sharp knife (run it under hot water and dry it off) and slice it into bars. Enjoy!