Melt butter in a large stockpot or Dutch oven over medium high heat. Add onion and fennel. Cook, stirring occasionally, until tender, about 3-4 minutes.
Stir in tomato paste, garlic, oregano and red pepper flakes until fragrant, about 1 minute.
Stir in wine, diced tomatoes, vegetable stock, clam juice and bay leaf. Bring to a boil; reduce heat and simmer until flavors have blended, about 15 minutes; season with salt and pepper, to taste.
Stir in clams and mussels. Reduce heat to low; cover, with a tight-fitting lid, and cook until the clams and mussels are just beginning to open, about 3-4 minutes.
Stir in cod or halibut, shrimp and scallops. Reduce heat and simmer until cod or halibut, shrimp and scallops are just cooked through and clams and mussels have opened completely, about 3-4 minutes. Discard any unopened clams.
Stir in parsley; season with salt and pepper, to taste.
Serve immediately.
Notes
Choose a wine you will drink. A dry white wine (pinot grigio or sauvignon blanc) is great here – it does not have to be anything fancy or overpriced. Just something you don’t mind sipping on since you will have an open bottle.
Use a blend of seafood and shellfish. A mixture of clams, mussels, white fish, shrimp, scallops, squid and dungeness crab are all great options.
Soak the clams. This is key to clean off all the sand and grit from the clams.
Check over the mussels. Rinse and scrub the mussels, and debeard as needed. Although farm-raised mussels will already come debearded, it’s still a good idea to do a once-over, discarding any mussels that are open or have cracked shells.
Avoid storing the mussels in water prior to cooking. Uncooked mussels should not be stored in water or in an airtight container as they need to breathe. The uncooked mussels can be placed in a bowl, covered with a damp dishtowel, in the fridge for 1-2 days.
Prep the scallops. Although safe to eat, gently peel away the small side muscle from the scallops as it is tougher and chewier than the rest of the scallops. Rinse and pat dry.
Use dry scallops. Dry scallops are generally preferred over wet scallops as the latter is treated with preservatives, retaining excess water.
Add the seafood in stages. To avoid any overcooking, add the shellfish first (clams and mussels), then finish with quick-cooking fish, shrimp, and scallops.
Make ahead of time. Cioppino is a great dish to make ahead of time, cooking the broth just before adding the seafood and storing in the fridge.
Serve with crusty bread. Serve with all the homemade crusty bread for dipping, sopping and dunking!