Pat the meat dry and rub on the salt and pepper. Cover tightly with the rosemary sprigs on the meat and marinate over night in the fridge. Bring the meat to room temperature for 2 hours prior to cooking.
Place the meat on a roasting rack to allow the juices to drip off and place in the middle of the oven on 230 C for 20 minutes. Then take out the oven and let the oven cool.
While the meat is roasting, heat olive oil in a pan over medium high heat. When the oil is hot add in the onion and garlic and cook till soft. Then add the jam, water or stock and port. Bring to a boil and reduce down to about 1 ½ cups.
Turn the oven down to 180 C, brush the meat with the glaze and continue to cook the meat. Brush the meat with the glaze every 10 minutes until the middle of the meat reaches 50 C.
Remove meat from oven, loosely cover and leave to rest for 30 minutes.
