In a 3 1/2 to 6 quart crockpot, combine stew beef, carrots, celery, onions, tomatoes, mushrooms, wine or beef broth, salt, thyme, mustard, and pepper. Cover and cook on LOW 8 to 10 hours, (or HIGH 4 to 5 hours) or until vegetables and beef are tender. Comin water and flour; gradually stir into beef mixture. For herb dumplings, mix baking mix, thyme, sage, and rosemary. Stir in milk just until moistened. Drop dough by spoonfuls onto hot beef stew mixture. Cover and cook on HIGH for 25 to 35 minutes or until toothpick inserted in center of dumplings comes out clean.