Butter the cake pan of your choice, then press wax paper over the bottom of the pan.
If using Dairy Queen ice cream, spread it in the bottom of the pan. If you are using any other ice cream, allow it to soften, then spread on the bottom of pan until the pan is almost half full. Sprinkle with crushed Oreo cookies, then spoon hot fudge sauce (at room temperature) over the top of this. Set in freezer until frozen.
Remove from freezer and add second layer of ice cream. Smooth it evenly with the top of the cake pan. Return to the freezer and freeze until very hard.
Remove from freezer and frost with a mixture of equal parts ice cream and thawed frozen whipped topping beaten together. Return to freezer until serving time.