Add onion to pot.
Combine water, catsup, sherry, garlic, mustard, marjoram, rosemary and thyme. Add to meat with bay leaf. Simmer, covered, for 2 hours or until tender.
Remove meat and set aside. Remove bay leaf; skim off any excess fat. Add mushrooms.
For gravy, combine cold water and flour until dissolved. Stir into juices and cook until thick and bubbly.