- In a large stock pot, bring the fish stock to a low boil. Reduce the heat and simmer 20 to 25 minutes. Set aside until needed.
- Make the marinate for the fish in a plastic zip lock bag by mixing 6 tablespoons of olive oil and three chopped garlic cloves. Soak the saffron threads in a couple of tablespoons of hot water and add to the olive oil garlic mixture. Cut the fish in into 2 inch cubes and add to the marinade. This can be done one day ahead of time.
- Heat ⅓ cup of olive oil in a stock pot on medium heat. Add the onions, leeks and chopped fennel and sauté until soft, taking care not to brown, about 10 minutes. Add 4 to 5 garlic cloves and sauté a minute more. Add the tomatoes, orange zest, a bunch of the fennel fronds, and the orange rind. Bring to a simmer, reduce heat, and cook 10 minutes. Taste the broth. Add the fish stock and remaining saffron to the tomato sauce. Bring to the boil, reduce heat, and simmer. Season to taste with salt and pepper, remembering that seafood will be added.
- Meanwhile, make the garnish by toasting the croûtes. Make rouille by adding one tablespoon of the tomato paste to the mayonnaise, along with the lemon juice, red wine vinegar and the chopped hot pepper or hot sauce. Top each croûtes with one to two tablespoons of rouille.
- When ready to eat, add the thickest pieces of the fish to the simmering soup and cook a few minutes, without letting it come to a boil. Add shrimp, crabs and the thinner or more delicate fish, such as flounder, and cook a minute or two in the simmering soup. Add the clams and any remaining scraps of fish. Cook until the shrimp and crabs are pink and the clams open. Taste and season with salt, pepper, and Pernod or anise liquor.
- Ladle all the seafood from soup onto a platter and Sprinkle with chopped fennel frond if desired. Serve the broth in a separate terrine or mix with the seafood platter. Garnish with one to two croûtes and serve immediately.