Heat olive oil in a Dutch oven or large heavy pot over medium heat. Add onion and next 6 ingredients; cook, stirring occasionally, 6 to 8 minutes or until vegetables are tender.
Add wine; increase heat to medium-high, and bring mixture to a boil. Add mussels and cook, covered, shaking gently once or twice, 3 to 5 minutes or until mussels open. (Discard any that do not.) Transfer mussels into serving bowls using tongs.
Stir crème fraîche into vegetable mixture. Ladle vegetables and cooking liquid over mussels, and serve with crusty bread.
