PreparationFor broth: Heat oil in a large heavy pot over medium heat. Add onion and cook, stirring occasionally, until softened, 8-10 minutes. Add garlic, basil, oregano, and red pepper flakes; stir until fragrant, about 3 minutes. Remove pot from heat and add wine. Return pot to heat, bring to a boil, and cook until wine is reduced by half, about 4 minutes. Add tomatoes with juices, crushing with your hands as you add them. Cook, stirring occasionally, until thickened, 15-20 minutes. Add clam juice, parsley, bay leaves, and 8 cups water; season with salt and pepper. Bring to a boil, reduce heat, and simmer until flavors meld, 10-15 minutes more. Discard parsley sprigs and bay leaves. DO AHEAD: Broth can be made 2 days ahead. Let cool slightly; chill until cold. Cover and keep chilled. Reheat before continuing. For soup: Heat oil in a large heavy pot over medium heat. Add shallot; stir often until softened, about 3 minutes. Add garlic; stir until fragrant, about 1 minute. Remove from heat; add mussels and wine. Set over medium-high heat, cover, and cook, stirring occasionally, until shells open (discard any that do not open), about 4 minutes. Add reserved broth; bring to a simmer. Add fish and shrimp. Cover; cook just until opaque, about 4 minutes. Stir in butter; season with salt and pepper. Divide among bowls; top with parsley. Serve with toast.
PreparationFor broth: Heat oil in a large heavy pot over medium heat. Add onion and cook, stirring occasionally, until softened, 8-10 minutes. Add garlic, basil, oregano, and red pepper flakes; stir until fragrant, about 3 minutes. Remove pot from heat and add wine. Return pot to heat, bring to a boil, and cook until wine is reduced by half, about 4 minutes. Add tomatoes with juices, crushing with your hands as you add them. Cook, stirring occasionally, until thickened, 15-20 minutes. Add clam juice, parsley, bay leaves, and 8 cups water; season with salt and pepper. Bring to a boil, reduce heat, and simmer until flavors meld, 10-15 minutes more. Discard parsley sprigs and bay leaves. DO AHEAD: Broth can be made 2 days ahead. Let cool slightly; chill until cold. Cover and keep chilled. Reheat before continuing. For soup: Heat oil in a large heavy pot over medium heat. Add shallot; stir often until softened, about 3 minutes. Add garlic; stir until fragrant, about 1 minute. Remove from heat; add mussels and wine. Set over medium-high heat, cover, and cook, stirring occasionally, until shells open (discard any that do not open), about 4 minutes. Add reserved broth; bring to a simmer. Add fish and shrimp. Cover; cook just until opaque, about 4 minutes. Stir in butter; season with salt and pepper. Divide among bowls; top with parsley. Serve with toast.