To butterfly & brine pork: You're going to double butterfly the pork loin so it can be flattened, stuffed and rolled. To do that, you'll make two long horizontal cuts, one on each side, dividing the roast in thirds without cutting all the way through. Place the roast on a cutting board. Holding the knife blade flat, so it's parallel to the board, make a lengthwise cut into the side of the roast just above the center, stopping short of the opposite edge so that the flap remains attached. Rotate the tenderloin 180 degrees . Still holding the knife parallel to the cutting board, make a lengthwise cut into the side opposite the original cut, just below the center, taking care not to cut all the way through. Open up the two cuts so you have a large rectangle of meat. Cover with a sheet of plastic wrap and pound to an even thickness of about 1/2 inch. Place the butterflied pork in the brine, adding more water to cover, if necessary. Cover and refrigerate for at least 2 hours and no more than 4 hours.