1. For the stuffing, preheat the oven to 200°C, gas mark 6. Melt 15g of the butter in a frying pan, and gently fry the fennel, onion and garlic for 5 minutes until beginning to brown. Crumble in the bread, and leave to cool.
2. Unroll the pork and spread the stuffing on top. Reroll the joint and tie with string. Place in a roasting tin skin side up. Combine the fennel seeds and sea salt, and rub over the surface of the pork, pushing it into the scored skin.
3. Roast for 30 minutes. Reduce the oven temperature to 160°C, gas mark 3, and roast for a further 1½ hours.
4. While cooking, combine the remaining butter with the ginger and lemon zest. Cut a thick horizontal slice off the top of each pear and reserve. Scoop out the core area of each and fill with the butter mixture. Replace the lids.
5. Add the pears to the roasting tin with the fruit juice, and return to the oven for a further 1 hour or until the pears are very tender and the pork is thoroughly cooked with no pink meat. Cover with foil and leave to rest in a warm place for 20 minutes before serving.