This is simple, the day before you brew just clean and sanitize your fermenter, pour 2 gallons of bottled distilled or spring water in it, close the lid and cover the airlock hole then put it in the freezer
The next day when your wort is done you just pull your fermenter out of the freezer, open it up and pour your boiling wort over top....it will be down to 70 degrees in less than 10 minutes