1. Place the lamb in a roasting dish and using a sharp knife, score its surface.
2. Mix together the balsamic vinegar, honey, garlic and rosemary, smearing over the surface of the lamb. Leave to marinade for as much time as you have, chilled.
3. Preheat the oven to 180 degrees C. Roast the lamb, basting, until cooked to your preference. I find about 90 minutes plus 15 minutes resting gives a slight pink, moist result.
Hint: Because of the balsamic vinegar and honey, the juices do caramelize so no gravy so a salsa is an ideal accompaniment.