One can either cook a whole roll or individual noisettes; a whole roll is good if you prefer cooking a single joint in the oven to fiddling with individual portions on the hob at the last minute (I definitely do), and it is nice to have the crisp outside and the pink, juicy centre, however, it doesn't look so good as it is apt to unfurl when you slice it to serve. Whichever you choose, both are suitable for a meal when you are not quite certain when people are going to show up, as you can start the cooking when they arrive and be eating the main course in under an hour. I hate having to try and keep things warm and stop them from spoiling whilst waiting for people, as they never comes out exactly as you hoped, but equally, one doesn't want to keep everyone waiting an age for dinner to be done.
The treatment I gave my hunk of tasty Jacob was what I almost invariably end up doing to joints of lamb: marinading in wine with redcurrant jelly, rosemary and garlic. Not terribly original, admittedly, but it works beautifully. The following was polished off by four, with buttery new potatoes and a generous quantity of asparagus.
Chop the rosemary leaves finely and put in a bowl with the wine and jelly. Cut each garlic clove into two or three chunks and crush each chunk with the flat of the knife's blade, then add to the rest of the marinade ingredients. Stir to combine. If the jelly refuses to dissolve into the wine, zap it in the microwave for a few seconds. You should be able to get the jelly to soften a bit without actually making the liquid hot, if this should happen, just leave it on the side to cool down. Once you have a fairly well combined, cool marinade put the meat in a large freezer bag and pour in the marinade. Seal the bag with as little air in it as possible and place in the fridge, on a large plate in case of leakage, until a couple of hours before you want to cook it.
At least an hour before you want to cook the meat, take it out of the fridge to come to room temperature.
Preheat the oven to 200°C. Place the lamb in a roasting tin and rub with the oil. Strain the marinade into a jug then pour about a third into the roasting tin; reserve the rest. Add cold water to the tin so that there is about 2mm depth tof liquid (ie a thin layer coating the entire bottom). Bake at 200°C for 15 minutes and then reduce the heat to 180°C. Baste with the pan juices and then roast for a further 25-35 minutes, depending on how pink you like it.
Once the meat is cooked, remove to a warm serving plate and cover with foil to keep it hot whilst you make a gravy. Strain the juices from the roasting dish into a small saucepan and add a teaspoon of the flour. Whisk until it is combined and there are no lumps visible. Add the reserved marinade and bring to the boil, stirring constantly. If the gravy is very thin, carefully whisk in the rest of the flour and heat again until thickened. If any lumps do form, just strain though a sieve. Serve the sauce in a jug alongside the meat, carved into thick rounds.