I see that my technique for cooking lamb boulangère has not changed very much since I last wrote about it, seven years ago. The chief difference is that yesterday I covered the roasting tin with foil, having learned that the lowest temperature of my oven – 130C-plus – is higher than the temperature inside a covered receptacle.
I smeared a little oil over a whole shoulder of lamb, seasoned it, and laid it on a bed of two sliced onions, the unpeeled cloves from a head of garlic, and two sprigs of rosemary. I covered the roasting tin with foil, and put it into the centre of a gas mark 1/140C oven, at 8am. (It’s a good idea to check on progress after the first hour, and regularly thereafter, adjusting the heat if necessary. I can never be confident about how my oven will behave.)
At 11am, I scraped and sliced new potatoes, dropping them into a pan of cold water. I brought the pan to the boil, and allowed it to boil vigorously for one minute before draining. (The idea is to get rid of some of the surface starch – potatoes cooked around meat are particularly liable to stick, because of the caramelised juices.)
By this time, there was a good amount of sauce surrounding the lamb. I removed the meat to a board, discarded the onions, squeezed the garlic out of its skins into the sauce, tipped in the potatoes and stirred them, and put back the meat on top.
I returned the tin, covered again, to the oven, turning up the dial to gas mark 4/180C. (I checked after half an hour, and discovered that this setting was high enough but not too fierce. The extra ingredients appeared to have moderated the temperature.)
At 1.30pm, I removed the joint to a large plate, covering it with the foil. I returned the potatoes to the top of the oven, now at its highest setting, to brown – about 20 minutes. (Be careful that they do not stick and burn.)
The meat fell away from the bone. I cut it up in the kitchen, and poured the small amount of sauce that the potatoes had not absorbed on top.