Preparing the fish. The fish should be cleaned, gutted and scaled. You can then fillet the fish. Cut the fillets in halves or thirds depending on the size. Reserve heads, fins, and carcasses. Remember: do not allow contact between the cut sides of fish fillets and fresh water. If using lobster remove the tail (and halve) and the claws and reserve in the fridge. Split the lobster in half length-wise and clean the inside of the lobster head. Wash clams.
For the fish stock, cook sliced onion in butter in a stockpot for about 5 minutes. Add fish heads, fins, and carcasses (and lobster body if you're using one) along with 6 cups cold water and the white wine. Add 1 of the bouquet garni. Simmer (low) this for about 2 hours.
While the stock is cooking, marinade the fillets in 1/4 cup olive oil with a pinch of the saffron threads and half of the garlic in a large bowl. Cover with plastic wrap and allow for at least 2 hours of marinade time.
Once the stock has completed cooking, strain with a fine sieve or colander. Be sure to squeeze as much juice from the bones and meat as possible. Reserve one half cup of broth for the rouille. Wash the stockpot so that it can be used again to make the soup.
For the soup, heat the other 1/4 cup olive oil over medium heat and add remaining onion, along with leeks, celery and carrot. Cook for about 10 minutes. Add tomatoes, the remaining garlic, orange peel, 1/4 teaspoon saffron, and fennel to the pot. Add the fish stock and (low) simmer for at least 40 minutes partially covered. About 20 minutes before you are finished, add the potato quarters.
While the soup is cooking, make the rouille. Soak the bread pieces in the reserved stock. Squeeze the juice out and place bread in food processor. In a mortar and pestle, smash the garlic and salt into a paste. Add the paste in the food processor. Add red pepper, saffron, and egg yolk to food processor. Blend and simultaneously drizzle oil into the mixture. The rouille (it's just a fancy French mayo) should then be refrigerated for about an hour before using and keeps up to a week.
Once the soup is finished you can cook the fish. First remove the potato and keep warm. Strain the soup again and return to the pot. Bring to a very rapid boil/ "boiling like mad" -- this is to help the oils emulsify. Add lobster tail and claws first -- cook for 1 minute. Then add clams and oily fish -- cook for 1-2 minutes. Then add white fish fillets -- cook for 2-3 minutes. Serve now!
Serve in large shallow bowls. Place one slice of bread in the bottom of each bowl. Place fish and shellfish on top of bread along with a few pieces of potato. Ladle soup over the top of the fish and bread. Pass rouille (add some to soup and/or spread on your bread) and serve with extra French bread.