Moules au champagne et au safran (ou pas)
- one pinch saffron threads (optional)
- 1.8 kilograms (4 pounds) fresh, live mussels, about 2.5 liters (see note)
- 15 grams (1 tablespoon) butter
- 4 small yellow onions, about 250 grams (9 ounces), finely minced
- 1 clove garlic, finely chopped
- 240 ml (1 cup) dry champagne, or other dry white wine, sparkling or not
- freshly ground black pepper
- 2 handfuls flat-leaf parsley, snipped
- 2 to 4 rounded teaspoons crème fraîche, or sour cream