1. If you bought a rolled lamb breast, unroll it for marinating. Pick a handful of grapes off the bunch and blitz them in a blender or food processor with all the marinade ingredients.
2. Pour the marinade into a large shallow dish and add the lamb, folded in half or three. Turn it over several times to coat well. Cover the dish with cling film and place in the fridge overnight.
3. Bring the meat to room temperature before cooking. Lift it from the marinade and pat dry; unroll it on a large chopping board. Sieve the marinade into a small saucepan for the sauce.
4. You can use dried rosemary to season the lamb but ground fresh rosemary is gorgeous: just blitz the stripped leaves in a coffee or spice grinder with a teaspoon of salt or breadcrumbs. It will keep in a spice jar for a good few weeks.
5. Preheat the oven to 170C/325F/gas 3. Sprinkle the lamb on the inside with salt, zest, pomegranate molasses or powder if using and about a heaped teaspoon of the rosemary powder. Spread the raisins evenly over the meat.
6. Roll up the breast tightly from the short edge into a very fat, short sausage. Tie it well with kitchen string.
7. Place it in a roasting dish with a cup of water, cover with a lid or tightly with aluminium foil and roast for 3 ½ hours. Take off the lid or the foil and roast for the final ½ hour uncovered. Remove from the oven and let it rest for about 15 minutes, loosely tented with foil.
8. Cut the grape stalk into several small bunches and place them on a small roasting tray brushed lightly with oil. Roast them for 15 minutes while the lamb is resting, until the start to split and wrinkle.
9. Prepare the sauce: bring the sieved marinade to the boil and cook down vigorously for 5 minutes. Take it off the heat and beat in the butter with a whisk. Taste and add the jelly if the sauce is too tart.
10. Cut off the string and slice the lamb thickly. Arrange it on the plates and serve with the roasted grapes and the sauce.