These flavorful, tender, fall-off-the-bone lamb shanks are browned in olive oil, then slowly cooked in a slow cooker with broth and aromatics until very tender. To quickly thicken the sauce, allow it to boil and then sprinkle a tablespoon of flour and keep whisking until it thickens. If you prefer to avoid flour, keep the cooked lamb shanks warm and reduce the sauce by boiling, as outlined below.