Line a 9 x 13 inch baking dish (see note below) with parchment paper. Set aside.
In a medium bowl, whisk together instant pudding and cocoa powder. Add half-and-half and mix until thickened. Fold in half of Cool Whip (8 ounces) and sprinkles. Set aside.
Add a single, even layer of ice cream sandwiches to the bottom of your dish. Trim sandwiches as needed to cover the bottom with no large gaps. (I did 2 rows of 4 sandwiches, and one and ⅓ sandwiches at the top.)
Spread ¼ cup of the fudge evenly over the sandwiches.
Add the chocolate mixture and spread into an even layer.
Place in freezer for at least 20 minutes (so sandwiches don’t sink into chocolate pudding.)
Remove from freezer and repeat the layers with a second layer of ice cream sandwiches and hot fudge sauce.
Finally, spread the remaining Cool Whip on top.
Freeze until firm, at least 2 hours.
Before serving, top with additional sprinkles and any other desired toppings (chopped up candy bars, M&Ms, caramel drizzle, etc). Slice and serve immediately.
Notes
I highly recommend using an extra deep 9 x 13-inch dish for this recipe so that you can cover the cake without smooshing the top. If you don't have a deep enough pan you can wait to add the final cool whip layer until 30 minutes before serving and freezer uncovered for those last 30 minutes.