Remove the meat and add the carrots and shallots to the casserole dish. Allow to brown for a couple of minutes then sprinkle in the flour. Mix this for 1 minute then return the lamb shanks to the dish along with the bouquet garni and the stock or water. Cover and bring to the boil, then reduce the heat. Leave to simmer on a very low heat for at least 1½ hours, turning the shanks occasionally. The meat should be very tender after this time.