Heat a large heavy-bottomed pot or Dutch oven over medium heat. Add 4 tablespoons olive oil. When shimmering, add the chopped onion, sliced fennel and diced red pepper. Season lightly with a pinch of salt. Cook, stirring occasionally, until the vegetables are softened and translucent, about 6–8 minutes.

Add garlic and tomato paste

Add the minced garlic and cook 30–60 seconds until fragrant. Stir in the tomato paste and cook 1–2 minutes, stirring, until it darkens slightly to deepen the flavor.

Deglaze and simmer

Pour in the white wine to deglaze, scraping up any browned bits. Let the wine reduce by half, about 2–3 minutes. Add the crushed tomatoes, passata (if using), fish stock, Calabrian chili or red pepper flakes, dried oregano, salt and black pepper. Bring to a gentle simmer, reduce heat to low, and simmer uncovered 15–20 minutes to meld flavors. Taste and adjust seasoning.

Seafood

Prepare seafood

While the broth simmers, rinse and pat dry the fish chunks and shrimp. Keep mussels and clams cold until ready; discard any with cracked shells or that do not close when tapped.

Add firm fish and shellfish

Increase heat so the broth is at a lively simmer (not a hard boil). Gently add the white fish chunks to the pot and simmer 3–4 minutes.

Add mussels and clams

Add the mussels and clams, cover the pot, and cook 4–6 minutes until shells open. Stir once gently midway. Remove any mussels or clams that remain closed after cooking.

Finish with quick-cooking seafood

Add the shrimp, scallops and calamari rings. Cover and cook for 2–3 minutes until shrimp are pink and opaque and scallops are just cooked through. Take care not to overcook the seafood—total cooking after adding these should be brief.

If you want a brothier stew

You may add up to 1/2 cup more warm fish stock or reserved clam juice if the stew seems too thick after seafood is added.

Aromatics & Finishing

Finish flavors

Turn off the heat. Stir in the lemon juice, lemon zest, chopped parsley and torn basil. Add 2 tablespoons extra-virgin olive oil and gently swirl to emulsify and gloss the broth. Taste and adjust salt, pepper or lemon as needed.

Serve

Ladle the seafood and broth into warmed shallow bowls. Sprinkle with additional parsley and a light dusting of grated Pecorino or Parmigiano if desired. Serve immediately with thick slices of crusty bread for dipping.

Make-ahead and storage notes

The base broth can be made 1–2 days ahead and refrigerated; add seafood and finish just before serving. Leftovers with seafood will keep 1–2 days in the refrigerator; reheat gently over low heat to avoid overcooking—better to reserve broth separately and add fresh-cooked seafood on reheating.