Place the saffron in a small bowl, add ½ cup boiling water, and set aside. In a large pot, heat the oil over medium heat. Add the leek, celery, onion, fennel, and garlic. Cover and cook for about 5 minutes to wilt the vegetables. Add the bay leaf, thyme, tomatoes, clam juice, wine, and fennel seeds. Bring to a simmer and cook, covered, for about 5 minutes.

Add the saffron and its soaking liquid and simmer, uncovered, for about 15 minutes more.

Remove the bay leaf.

Bring back to a steady simmer and add more wine if needed. Season to taste with the salt and pepper.

Add the mussels, cook for 5 minutes, then add the shrimp. Cook another 5 minutes, then add the fish. Reduce the heat to very low and simmer until the mussels have opened and the shrimp and fish have cooked through. Remove any mussels that haven’t opened. Check the seasoning, adding some red chile flakes if desired and an extra drizzle of oil. Serve with croutons or crusty bread.