Preparation Cut onion halves crosswise into less than 1/16-inch-thick slices with slicer. 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. 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.
Preparation Cut onion halves crosswise into less than 1/16-inch-thick slices with slicer. 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. 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.