In a 7 to 8-quart kettle simmer lamb, parsley, thyme, and salt and pepper to taste in 4 cups broth, covered, 1 1/2 hours. To lamb mixture add potatoes, onion, carrots, celery, and remaining 2 cups broth and simmer, covered, 1 hour.
In a small bowl whisk together flour and oil until smooth and stir into simmering stew until well incorporated. Simmer stew, uncovered, until thickened, 3 to 5 minutes, and season with salt and pepper.
Recipe courtesy of Gourmet Magazine