In a Dutch oven, brown meat on all sides, fat side first; remove meat. Add onions to drippings and saute until tender. Add bouillon, water, bay leaves, pepper and meat. Bring to a boil; cover and simmer 1 1/2 hours. Remove meat to a cutting board. With a sharp, long-bladed knife, slice across grain into 1/4" slices. Lift fat from broth. Add meat to broth and bring to a boil. Reduce heat and simmer 30 minutes or until meat is almost tender. Add carrots and potatoes. Cover and cook over medium-low heat about 30 minutes or until meat and vegetables are tender. Add salt. Discard bay leaf. Arrange meat and vegetables on a warm serving platter and spoon on some broth. Sprinkle with parsley. Mix horseradish and mayonnaise together and serve with meat. ----