In a large pot, melt the butter over low heat. Add the shallots, garlic, celery and thyme. Gently sauté for about 15 minutes, until the vegetables are soft but not browned. Add the wine, pepper and créme fraîche and raise the flame to high. Once the liquid comes to a boil, add the mussels, stir gently, lower the heat to a simmer and cover with a tight-fitting lid. Cook for 3 minutes, or more, or until the mussels open.

Add the parsley and stir gently. Transfer to a large bowls discarding any unopened mussels Serve with plenty of crusty bread for dipping.