Trim fat from meat. In a 6-quart Dutch oven brown meat on all sides in hot oil. Drain fat. Add beef broth, leeks, basil, marjoram, the 1/2 teaspoon salt, the 1/2 teaspoon pepper, and bay leaf. Bring to boiling; reduce heat. Cover and simmer for 1-1/4 hours.
Cut squash in half lengthwise; discard seeds. Cut each half into 4 pieces. Add squash to meat mixture. Then add parsnips, carrots, and mushrooms. Return to boiling; reduce heat. Cover and simmer for 20 to 25 minutes more or until vegetables and meat are tender. Remove meat and vegetables from Dutch oven; keep warm. Discard bay leaf.
For sauce, skim fat from pan juices. Measure 1-1/2 cups pan juices. Stir cold water into flour; stir into reserved juices in Dutch oven. Cook and stir until thickened and bubbly; cook and stir for 1 minute more. Season to taste with salt and pepper. Serve sauce with meat and vegetables. Makes 8 servings.