Melt the butter in a large heavy-based saucepan, add the shallots or onion and cook gently for 5 minutes until tender, but not coloured. Add the garlic, bay leaf and parsley stalks and cook for a further minute.
Pour in the wine and bring to a rapid boil. Add the mussels, all at once, and immediately cover the pan with a tight-fitting lid. Cook over a moderate heat, shaking the pan occasionally for 3–5 minutes until the mussels have opened. Discard the bay leaf, parsley stalks and any mussels that have not opened.
Strain the cooking juices through a fine-meshed sieve into a small saucepan. Add the crème fraîche or cream and 1 tablespoon of the chopped parsley and boil for 1–2 minutes to reduce slightly. Season with black pepper.
Transfer the mussels to a warmed serving dish or individual bowls. Pour over the hot sauce, sprinkle with the remaining parsley and serve straight away with slices of bread.
Choose wine that you enjoy drinking; it is a false economy to buy cheap ‘cooking’ wine as this spoils the flavour of the dish. Alternatively, dry cider works well in this dish.