3 Tbsp olive oil
1 large fennel bulb, thinly sliced
1 onion, chopped
3 large shallots, chopped
2 teaspoons kosher salt, or less to taste
4 large garlic cloves, finely chopped
1/2 tsp dried crushed red pepper flakes, or more to taste
1/4 cup tomato paste
1 28-ounce can diced tomatoes in juice
1-1/2 cups dry white wine
5 cups fish stock, or part bottled clam juice and part chicken broth*
1 bay leaf
1 lb littleneck or manila (or other small size) clams, scrubbed
1 lb mussels, scrubbed, debearded , OR l lb dry sea scallops
1 lb uncooked "large" shrimp (26-30 size), peeled and deveined
1/2 lb halibut or mako shark, cut into 2-inch chunks
1/2 lb cod (the thick loin), cut into 2-inch chunks
1/2 lb salmon (skinless fillet), cut into 2-inch chunks
Rough-chopped flat-leaf parsley, for garnish (optional)
Heat the oil in a very large nonreactive stockpot over medium heat. Add the fennel, onion, shallots, and salt, and sauté until the onion is translucent, about 10 minutes. Add the garlic and red pepper flakes, and sauté 2 minutes. Stir in the tomato paste, tomatoes with their juices, wine, fish stock* and bay leaf. Cover, and raise the heat just until the soup comes to a low boil. Reduce the heat to medium-low. Cover and simmer until the flavors blend, about 30 minutes. (Can be made ahead up to this point; refrigerate or freeze.)
Add the clams** and mussels to the cooking liquid. Cover and cook until the clams and mussels begin to open, about 5 minutes. Add the shrimp and fish. Simmer gently until the fish and shrimp are just cooked through, and the clams are completely open, stirring gently, about 5 minutes longer (discard any clams and mussels that do not open). Season the soup to taste, with more salt (if needed, but probably won’t be) and red pepper flakes (ditto!). Top with parsley. Ladle the soup into bowls, add some giant homemade croutons, and serve.
*To make your own quick fish stock, simmer 16 oz. bottled clam juice, 1 quart low-sodium chicken stock, and the shrimp shells in a small sauce pan for 15-20 minutes. Strain out the shells.
**NOTE: if using littlenecks, put them into the broth after the broth has been cooking for 15 minutes. Littlenecks take much longer to cook than manila clams, so you’ll need to give them a head start.