Soak salt cod overnight. Drain and cut into large cubes.
Sauté sliced onions and leeks in olive oil until transparent. Simmer tomatoes in butter until smooth. Fill a large saucepan with water; add vegetables with bouquet garni, orange peel, crushed garlic and saffron, and season to taste with freshly ground black pepper.
Bring to a boil; add sliced potatoes, and when they are half cooked, add cubed salt cod. Lower heat and simmer bouillabaisse until cod is tender.
To serve: place slices of stale French bread rubbed with garlic and sprinkled with grated cheese in individual soup dishes; pour over bouillon; serve cod and potatoes on a separate serving dish, sprinkled with finely chopped parsley.