Prepare brownies by combining the brownie mix, oil, water and eggs. Stir until well blended. Grease and flour two 9-inch cake pans, placing a piece of parchment paper in the bottom of each pan (use scissors to trim). Pour brownie batter into pans.
Bake in a 350°F oven for about 17-20 minutes. Remove from pans and cool completely.
In a small bowl, combine the hot fudge sauce (do not heat it) with the crushed cookies.
Place one layer of brownie cake in the bottom of a 9-inch springform pan. Top with the hot fudge and cookie mixture. Next, scoop out the cookies and cream ice cream and spread over the top of the hot fudge mixture. I removed the ice cream from the freezer for about 15 minutes to let it soften slightly for this step.
Finally, place the second layer of brownie over the ice cream and cover with foil. Freeze for about 2 hours (or more).
When ready to serve, remove the springform pan and cover the cake with the whipped topping. Add the reserved funfetti sprinkles from the brownie mix to the top of the cake. ENJOY.
Store remaining cake, covered, in the freezer for up to a week for best flavor.
Notes
Be sure to choose a brownie mix that makes enough to fill a 13x9 pan.
Store leftover ice cream cake covered in the freezer for up to 1 week.
Line your baking pans with parchment paper. For best results, use scissors to trim the parchment so it easily fits into your pans.