Prepare the brownies according to package directions. Spray a 9 x 13 pan with nonstick spray (OR for easiest removal, line with parchment paper) and bake the brownies according to package directions. Slightly underbake the brownies by 2-3 minutes.
Remove and allow the brownies to cool completely.
Coarsely chop all but 3 oreos. Place on top of the cooled brownies.
Warm the hot fudge for 30 seconds and then pour and smooth the hot fudge evenly over the brownies.
Place in the freezer for 10 minutes and remove the ice cream to soften a bit at this time.
Scoop large amounts of ice cream over the hot fudge. Evenly scoop out the entire container of ice cream over the hot fudge layer.
Smooth the ice cream down using a metal spatula until it is even. Freeze for 2 hours and preferably overnight.
Spread the whipped topping evenly over the ice cream and, if desired, garnish with three crushed up oreos (no need to remove the filling).
Cover and return to the freezer to 20-30 minutes.
Allow to sit out for a few minutes before slicing into bars.
Recipe time does not include chilling which does take a bit of time.