2) Meanwhile, cut the fennel bulbs in thick wedges, cutting through the core. Toss the fennel, carrots, potatoes, and onions in a bowl with the olive oil, melted butter, salt, and pepper to taste. Place the vegetables in a large roasting pan and cook for 30 minutes.
3) Add the pork loin to the pan and continue to cook for another 30 to 50 minutes, or until a meat thermometer inserted into the middle of the pork reads exactly 59C.
4) Remove the meat from the pan and return the vegetables to the oven to keep cooking. Cover the meat with aluminium foil and allow it to rest for 15 minutes. Remove the strings from the meat and slice it thickly.
5) Arrange the meat and vegetables on a platter. Sprinkle with salt and freshly ground pepper to taste and serve warm.