Just a small amount of precious saffron turns this weeknight supper into something out of the ordinary. We prefer cultivated mussels because they require less cleaning, making them a cinch to prepare.
Cook onion with saffron and 1/2 teaspoon salt in oil in a wide 6- to 8-quart heavy pot over moderately high heat, covered, stirring occasionally, until onion is softened, about 5 minutes. Add wine and bring to a boil, then stir in cream, pepper, remaining 1/4 teaspoon salt, and mussels.
Add wine and bring to a boil, then stir in cream, pepper, remaining 1/4 teaspoon salt, and mussels. Cook, covered, checking after 6 minutes and transferring opened mussels to soup bowls with a slotted spoon. (Discard any that remain unopened after 8 minutes.)
Stir parsley into broth and pour over mussels.