Cut fillets into small pieces.
Place half of the potatoes in a buttered baking dish and sprinkle with salt and pepper to taste, onion and bread crumbs. Dot with butter and anchovy bits. Layer the remaining potatoes over the top. Add the milk or cream, cover and bake 30 minutes in a preheated 350° oven. Uncover, reduce heat to 325 degrees and bake for another 30 minutes or until lightly browned.