Preheat oven to 350F/180C
Spread aluminium over the bottom of the oven tray, and pour the water in the base and lay the rack over the top.
Wash the pork then dry it completely with paper towels
Make 6 slits in the side of the pork below the layer of fat just under the skin, and slide in the cloves of garlic all the way
Rub the flesh side of the pork with Chinese 5 spice
Place the pork on the rack, skin side up, and pour on the salt.
Spread the salt evenly across the skin with the back of a spoon
Cook for 1 hour. If the pan goes dry add a little extra water to it. It's there to keep the meat moist. The salt is there to keep the skin dry.
The pork will shrink a little, and the salt layer will come away from the skin a little
Remove the salt and put the tray back in the oven at 465F/240C for 40 mins to crisp up the skin into crackling.
Take the pork out and leave it on the rack to rest for 10 mins before cutting
Put the pork on a board skin side down and cut with a cleaver into 1" cubes