Cook the salt pork very slowly in a small skillet until the fat has melted and the scraps are brown. Strain, setting aside the crisp scraps, and put 2 tbsp of the fat in a soup pot. Heat the fat, add the onions, and cook over low heat until golden. Stir in the potatoes and toss until well coated. Add the fish or clam liquid and simmer for about 5 mins. Cut the fish in chunks, add it to the pot, and simmer, partially covered, for about 10 mins, or until the fish is cooked through and the potatoes are tender. Stir in the cream or milk and heat slowly, without boiling. Add the pork scraps. Just before serving, stir in the butter, add s& p to taste and heat until butter melts.