The pork takes 24 hours to cook, which is no cause for alarm, because for about 23 hours and 55 minutes you are ignoring it absolutely. And it makes your house smell like a home should.
So, if you're planning to eat this for Sunday lunch, at about Saturday lunchtime, preheat your (clean) oven to the hottest it will go. Sit the pork skin-side-up on a rack over a roasting pan. I like to use a mortar and pestle to make my paste but you could just grate the garlic and ginger (a microplane grater is the tool for the job) and stir in chiles, a tablespoonful of oil and 2 of vinegar if you want. Otherwise, pound together the peeled chopped ginger and peeled cloves with the fresh chiles, adding a tablespoonful of oil and 2 of vinegar when they're squished and paste-like.
Using your fingers, rub this paste over the scored skin, pushing bits into the cut lines of the rind. Stagger across to the oven and put in the tray, leaving it for 30 minutes. Meanwhile, into the bowl in which you mixed the paste, pour the 2 remaining tablespoons each of oil and vinegar. When the pork's had its half an hour, remove it from the oven, and turn the temperature down to 225 degrees F. Now turn the pork over: I find it easiest to lift it by hand wearing oven mitts. It makes them dirty, OK, but there is the washing machine...
Pour the oil and vinegar over the underside (which is now uppermost on the rack) and put the pork back in the low oven, leaving it there for 23 hours. (Actually, you could leave it longer. One of the joys of this is that it cannot overcook.) Anyway, after 23 hours, or 30 to 40 minutes before you actually want to eat, turn the oven back to the highest it will go, remove the pork and turn it back crackling side up. Put it back in the oven for 30 minutes, in which time it will get hot and crisp, though you can give it another 10 if you feel it needs it.
Remove, slice off the crackling in a horizontal swipe of the knife and break it into manageable pieces, then start carving or pulling at the tender meat.
Recipe courtesy of Nigella Lawson, 2007