Preheat the oven to 325°. In a small bowl, mix the fennel, salt and pepper. Coat the pork all over with the spice mixture and set it in a large roasting pan, fat side up. Pour the olive oil around the pork. Roll the potatoes in the oil to coat and arrange them cut sides down. Roast for about 60-90 minutes, until the potatoes are tender and browned on the bottom. Transfer the roasted potatoes to an ovenproof serving bowl. Continue roasting the pork until the pork is very tender, about 3 hours.