Heat a large heavy pot over medium heat and add the Olive Oil. Once shimmering, add the Onion (finely chopped) and the Red Bell Pepper (diced) and cook, stirring occasionally, until softened and translucent, about 6–8 minutes.
Add the minced Garlic and cook 30–60 seconds until fragrant. Stir in the Crushed Tomatoes, Sweet Paprika and a pinch of the Saffron Threads (crush them between your fingers) along with the Bay Leaf; cook 4–5 minutes to meld the flavors.
Pour in the Dry White Wine to deglaze the pan, scraping up any browned bits, and let it reduce by half, about 2–3 minutes.
Add the Fish Stock, bring the mixture to a gentle simmer, and adjust heat so it maintains a light bubble. Taste and season lightly with Salt and Black Pepper; you can adjust seasoning later as seafood is added.
Add the Clams and Mussels to the simmering broth, cover the pot, and cook until the shells open, about 5–7 minutes. Discard any that remain closed.
When the shellfish are beginning to open, add the Squid (sliced into rings or bite-sized pieces) and the Shrimp. Simmer uncovered until the shrimp turn pink and the squid is just tender, about 3–4 minutes.
Gently add the chunks of Firm White Fish to the pot and poach in the simmering broth until opaque and flaky, about 4–6 minutes depending on thickness.
Turn off the heat, stir in chopped Flat-Leaf Parsley, adjust seasoning with additional Salt and Black Pepper if needed, and finish with a squeeze of Lemon to brighten the soup.
Ladle the sopa into bowls, making sure each serving gets a mix of shellfish and fish, and serve immediately with thick slices of Crusty Bread for dipping.
