Shoulder of Spring Lamb with Flageolet Beans and Olive Relish

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 nutt