I call this "Forever Roasted Pork" because it takes (almost) forever to roast — about eight hours. The meat is well seasoned and cooked in a slow oven until it is so tender it shreds. Once it's done, I challenge you not to stand at the kitchen counter and pick.
Thinly slice the onions on a mandoline or with a sharp chef's knife.
Heat the olive oil in a large sauté pan over medium heat until hot. Add the onions and a pinch of salt and pepper. Reduce the heat to medium-low and cook for about 1 minute. Add the sage and cook until the onions cease throwing off water, about 3 minutes. Add the water, cover, and cook until the onions are very tender, about 10 minutes. Uncover and sauté until the onions are very soft and the pan is dry again, about 2 minutes. Season well with salt and pepper.
Preheat the oven to 275°F. Peel back the pork skin and spread the onions directly on the fat layer. Fold the skin back over the onions and tie closed with kitchen string. Season well all over with the fennel spice.
Arrange the meat on a rack in a roasting pan and cook until the meat is very tender, 6 to 8 hours. It is ready when it pulls away easily if picked at with a pair of tongs. It is often easiest to cook the meat overnight, or put it in the oven in the morning and let it cook all day. It does not need to be attended.
Variations: This dish can be simplified or made more elaborate depending on your taste. You can omit the onions and simply season the meat with the fennel spice. You can roast aromatic vegetables until caramelized and add them to the bottom of the roasting pan. Or you can add another layer of flavor to the onions: mince fresh rosemary and fruits such as oranges, kumquats, Meyer lemons, apples, pears, or quince, and cook with the onions, or make a paste of garlic and fresh or dried chilies and add to the onions.
Chef's Note: For added flavor, baste the pork with roasted apple dressing during the last two hours of cooking.
