Heat the oil in a stainless-steel saucepan and brown the bacon well until it is crisp and golden.
Add the onion, cover and sweat for a few minutes over a low heat. Stir in the flour and cook for 1-2 minutes.
Add the fish stock or water gradually. Add the milk, bouquet garni and potatoes. Season well with salt, pepper, mace and cayenne.
Cover and simmer until the potatoes are almost cooked, approximately 5-6 minutes. (The chowder may be prepared ahead to this point.)
Cut the fish into 2.5cm /1in cubes. Add to the pot as soon as the tip of a knife will go through a potato.
Simmer gently for 3-4 minutes, stir in the cream and add the shellfish. Add any liquor obtained from opening the mussels or clams. When boiling, remove from the heat.
Taste, correct the seasoning and sprinkle with freshly chopped parsley and chives.
Serve in a deep dish with plenty of bread and butter.
Remember that the fish will continue to cook in the heat of the chowder so make sure it is not overcooked.
