Combine potatoes and carrots in a large saucepan. Add just enough water to cover vegetables Cook about 12 to 15 minutes, until tender. In a small saucepan, saute onion and celery in melted butter or margarine, until slightly tender. Add mushrooms and saute 2 more minutes. Drain liquid from potatoes and carrots. Add sauteed vegetables to potatoes and carrots. Stir in Braised Beef Cube Mix. Simmer about 15 minutes, until heated through. Serve hot.