Heat the oven to 425°F. Season the shanks with salt and pepper. In a large, high-sided ovenproof pot, heat the oil until barely smoking. Sear the shanks in batches on all sides until golden brown.
Put all the shanks in the pot; add the peppercorns, bay leaves, stock, wine, garlic, celery, carrots, onion, and mushrooms. Put the pot in the oven and cook, turning the shanks every 1/2 hour, until the meat is very tender but still on the bone, about 2 hours.
Remove the shanks and some mushrooms and onions and cover them with foil. Strain the braising liquid into a medium saucepan, degrease carefully, and simmer gently until its flavor is intensified and its volume is reduced by about a third. Serve the shanks on top of the white bean purée; ladle the sauce over the lamb. Serve some of the mushrooms and onions on the side.
Make Ahead Tips
You can braise the lamb shanks up to one day ahead of serving. Remove the shanks (and vegetables) from the cooking liquid, and refrigerate both separately. To reheat, remove the fat from the liquid and strain. Put the shanks, the vegetables and the cooking liquid in a covered roasting pan in a 400°F oven for about 20 min.
nutrition information (per serving):
16, Fat Calories
140, Saturated Fat
44, Monounsaturated Fat
4, Polyunsaturated Fat
Photo: Ben Fink