Preheat the oven to 325º
If using pancetta, cut it into strips about 1/4 inch wide. If using bacon, cut each strip into 3 pieces
Push strips of pancetta or bacon into meat, use a chop stick or comparable item . Fold bacon over the chopstick and push into meat.
Insert the cloves random into any of the places where the meat was larded.
Choose a heavy casserole with a tightly fitted cover, just large enough to fit the meat snugly.
Spread the sliced onions on the bottom of the pot, and over it the rest of the pancetta or bacon
Put in the meat, and season liberally with salt and freshly ground pepper. Cover tightly. Put the pot in the uppermost level of the preheated oven
Cook for 3 1/2 or 4 hours until the meat is very tender when pricked with a fork. Turn the meat after 30 minutes, and every 30 minutes thereafter. The onions should turn brown and the meat will acquire a a dark rich color.
When done, slice the meat on a carving board, and lay the slices on a warm serving platter. Pour the juices left on the carving boarding all the contents of the casserole over the meat, and serve at once