Wash and scrub the clams then place them in a large pan with a splash of water. Cover tightly and cook over a high heat. As soon as the clams are open, take the pan off the heat and drain them in a colander, saving the cooking liquor in a bowl. When cool enough to handle, remove the clams from their shells and cut the meat into 1cm/½in pieces.
Melt the butter in a pan then fry the diced pork or bacon, until it starts to brown. Add the onions and fry until softened.
Place the potatoes in a separate large pan with the milk, cream and bay leaf. Bring to the boil then reduce to a slow simmer until just cooked but still firm. Add the pork, onions and clam cooking liquor and simmer for a further five minutes then add the cod (pr pollack or coley) fillet. Simmer until the fish is cooked, then add the clams. Warm through then season with salt (if necessary) and freshly ground white pepper.
Pour the chowder into a serving tureen then garnish with the chopped parsley and crushed water biscuits.