Preparation Cook onion, bell pepper, leek, carrots, celery, chopped tomato, and garlic in butter in a 6-quart wide heavy pot over moderate heat, stirring frequently, until softened, about 10 minutes. Stir in stock and water and bring to a boil. Reduce heat and simmer briskly, uncovered, 20 minutes. Stir in fish, tomato paste, bay leaf, cheesecloth bag of allspice, thyme, hot pepper sauce, and salt and pepper to taste. Simmer 20 minutes (fish will break up), then restir cornstarch mixture and stir into chowder. Simmer, stirring occasionally, until thickened, about 2 minutes. Stir in clams, shrimp, Worcestershire sauce, and rum and gently simmer 30 minutes. Remove from heat and let chowder stand, covered, 1 hour. Gently return to a simmer and stir in Sherry pepper sauce.