Prepare the devil's food cake mix into two 8-inch round cake pans, let cool completely. Wrap with plastic wrap and place each layer in a large zip-close bag and place in the freezer. You'll save one for later and use one for this recipe.
Using the same size cake pan that you baked the cake in, line it with plastic wrap or parchment paper and place the softened ice cream in it and spread into an even layer. Top with plastic wrap and place back in the freezer until set.
Just before assembling the cake combine 10 finely chopped Oreo cookies and ALL BUT 1 tbsp of the hot fudge sauce in a bowl.
Place one layer of the chocolate cake on your cake stand (or large plate) and spread the hot fudge cookie mixture over the top in an even layer. Carefully place the ice cream layer on top and frost the cake with the thawed whipped topping.
Decorate the sides and top with the remaining cookies and hot fudge sauce. Place back in the freezer until set. Just before serving take the cake out and let sit at room temperature for 10 to 15 minutes for easy slicing. Enjoy!
This recipe makes two layers of chocolate cake, but only one will be used. Keep the other wrapped tightly in plastic and stored in the freezer for up to 5 months.