If using bone-in ribs, cut away the bones and set aside. Cut pork into 1-inch cubes, sprinkle the ribs evenly with the salt and allow to stand, refrigerated, for at least 1 hour and no more than 12 hours.
Move oven rack to middle position and heat oven to 325 degrees.
Dry pork cubes well and sprinkle generously with pepper. Heat oil over
medium-high heat in Dutch oven or other large, heavy pot until shimmering.
Working in batches to avoid crowding, brown the pork well (including bones if
you have them), transferring to a platter as browned, adding more oil in between
batches if needed.
Add the onions and fennel to the pot and cook, stirring frequently, until onions are transparent, 7 to 10 minutes.
Add the wine and bring to a simmer, stirring to dissolve any fond on the bottom of the pot. Add the pork (and bones if you have them), sweet potatoes, caraway seeds, allspice, bay leaves and enough chicken stock to just cover the meat. Bring to a simmer, cover and place in oven for 1 hour.
Add the pears to the pot, then continue to cook until meat is very tender, about 30 to 45 minutes more.
Remove bones from pot, stir in lemon juice, then serve stew in bowls, passing mustard separately so people can put a dollop on their stew if desired.