Add the fennel wedges, onion, celery, carrot and garlic to the casserole and cook over moderate heat until softened, about 5 minutes. Add the tomato paste and cook, stirring, for 2 minutes. Add the wine and bring to a boil. Add the chicken broth, thyme and bay leaf. Return the pork to the casserole and add any accumulated juices. Bring to a boil. Cover and braise in the oven for 1 hour. Remove the lid and cook the pork for 2 hours longer, adding the olives after the first hour. The pork should be very tender.