A meal in itself, this chowder should be made a day in advance of serving.
The day before you serve this chowder, bring water to boil in a soup kettle. Add fish and simmer, covered, 10 minutes or until tender. Remove fish, flake into small pieces, and discard skin and bones. Add onions to cooking liquid and simmer, uncovered, 5 minutes. Add potatoes and simmer, uncovered, 10 minutes. Return fish to kettle. Add milk, cream, butter, and salt and pepper. Heat soup slowly for 20 minutes before serving. Stir gently. Serve in large bowls with crackers.