Trim the lamb of fat and cut in cubes. Sear the lamb in a pan with no added fat. As it browns, strain and place in a casserole. Over a moderate heat, sprinkle with 2 tablespoons flour and stir until brown. Add the onions and the bouquet garni. Bring to a boil, then simmer covered. Brown the turnips slowly in the lard. Drain them and add to the stew. Add salt, and pepper. Cook for 1 hour and 15 minutes, then place the potatoes in the stew. The stew is ready when the potatoes are cooked. Degrease as necessary and serve on hot plates.
