True spring lamb is not easily found here, as most American lamb (sourced from New Zealand) is raised to a larger size. But some good butchers carry or can order it, and a few excellent American farms now specialize in young pastured lamb. Otherwise, ask your butcher for the smallest lamb shoulder roasts possible. Tender young spring lamb is best cooked almost medium, with a crisp, roasty exterior. I’m crazy about pale green flageolet beans, a classic lamb accompaniment. Their wonderful nutty flavor pairs well, too, with olive oil and thyme.
Pick over the flageolet beans and rinse them well. Set them to boil in a large heavy pot with enough cold water to cover by 3 inches. Add the onion, bay leaf, unpeeled garlic, and a large thyme sprig. When the water boils, turn the flame to low and let the beans simmer gently until quite tender, about 1 hour if they are from a recent crop, longer if not.
Once the beans are done, stir a good spoonful of salt into the cooking liquid, and let the beans cool in their broth. The beans can be cooked early in the day, or even a day ahead and refrigerated.
Preheat the oven to 375 degrees. Season the lamb roasts with salt and pepper. Insert the slices of garlic in the loose flesh on the underside of the roasts. Lay a few rosemary and thyme sprigs in the bottom of a roasting pan. Set the lamb on top. Drizzle a little olive oil over the lamb. Pour the white wine into the pan.
Roast the lamb for 45 minutes to an hour, or until the exterior is nicely browned and the internal temperature reads 130 degrees. Remove the lamb to a platter, cover loosely, and let it rest.
Scrape up the juices from the bottom of the roasting pan with a wooden spoon, taking care to dissolve the caramelized brown bits clinging here and there. Pour the pan juices through a fine-meshed strainer into a small saucepan. Skim off any surface fat, and reheat the pan juices just before serving.
Drain the flageolets, reserving their liquid, and put them in a shallow pan. Season them with salt and pepper, a little chopped thyme, and a good splash of fruity olive oil. Add a cup of the bean broth and reheat the beans gently.
Chop the parsley and slice the lamb.
Pour the flageolets onto a warmed platter and arrange the lamb slices over the beans. Spoon some of the warm pan juices over the lamb. Scatter the parsley over everything and serve. Pass the olive relish, thinned with pan juices if you like.