1 Rinse the mussels thoroughly and remove beards. Throw away the open shells. Peel and finely chop the garlic and onion. Rinse and chop the celery. Heat the oil in a skillet. Sauté the garlic, onion and celery until translucent. Stir in the wine. Season with salt and pepper to taste and stir in the saffron. Add the mussels to the broth and cook, covered, until the shells open, about 6 minutes. Discard any mussels that remain closed. Remove the mussels from the shells. Season the sauce with salt and pepper to taste and allow to cool completely.
2 Preheat a convection oven to 200°C (approximately 390°F).
3 Rinse the fish and pat dry. Season with salt and pepper to taste and place each on a large piece of parchment paper. Divide the mussels and vegetables from the sauce over the fish. Pour some of the sauce over the fish. Fold the paper inward and seal the ends with butcher's twine. Place the parcels on a baking sheet and cook for 15 minutes in the oven.
4 Open just before serving and garnish with basil.