1. Heat 1/2 cup of the oil and 8 tablespoons of the butter in a large pot over medium heat. Add onions and cook, stirring often, for about 2 minutes. Add carrots, celery, peppers, leeks and fennel and cook, stirring often, for about 5 minutes. Add crushed tomatoes, tomato paste, 4 cups water, bay leaves, oregano, thyme, basil and cayenne. Season to taste with salt and pepper. Bring to a boil, reduce heat to low, and simmer, stirring occasionally, for 2 hours.
2. Heat remaining 1/2 cup extra virgin olive oil, 8 tablespoons butter and garlic in a large, heavy skillet over high heat until fragrant, 1–2 minutes. Working in 2 batches, dredge snapper, oysters and large rock shrimp in flour, shaking off excess, and fry, turning seafood frequently until golden, 1–2 minutes. Transfer seafood with a slotted spoon to pot with sauce and add crabmeat, cover and simmer for 10–15 minutes.
3. Add wine to same skillet over high heat, scraping browned bits stuck to bottom of skillet. Add clams, cover, and cook until shells open, about 5 minutes. (Discard any clams that don’t open.) Add clams and broth to pot; adjust seasonings. Ladle soup into large bowls, garnish with parsley and serve with toasted sourdough bread if you like.