Heat oil in a Dutch oven over medium-high heat. Add leeks, celery, garlic and fennel seed and cook, stirring often, until the leeks are softened, 3 to 4 minutes. Add tomatoes and potatoes; cook, stirring often, until the tomatoes begin to break down, about 4 minutes. Add wine, increase heat to high, bring to a boil, and cook, stirring often, until reduced, 2 to 3 minutes. Add clam juice, water, orange peel, bay leaves and saffron and bring to a boil. Reduce heat and simmer, stirring occasionally, until the potatoes are just tender, about 15 minutes.

Carefully submerge tilapia and scallops in the soup, return to a simmer and cook for 2 minutes. Add calamari, submerge in the soup, and continue cooking until cooked through, about 3 minutes. Discard orange peel and bay leaves. Serve the soup with a spoonful of Spicy Rouille on top.

Tips: Bottled clam juice can be very high in sodium. We like Bar Harbor brand, which has 120 mg sodium per serving. Look for it in the canned-fish section or the seafood department of your supermarket.

Use a vegetable peeler to easily remove strips of the outer orange peel (zest), leaving the bitter white pith behind.

Saffron is the dried stigma of a saffron crocus. It contributes a pungent flavor and intense yellow color to classic dishes like paella. Saffron is sold in threads and powdered form.

We prefer cooking with dry sea scallops (not treated with sodium tripolyphosphate, or STP). Scallops that have been treated with STP (wet scallops) have been subjected to a chemical bath and are not only mushy and less flavorful, but will not brown properly.

Calamari, also known as squid, is sold frozen or fresh in the seafood department of the grocery store. Look for cleaned calamari, with its cartilage and ink removed; otherwise ask at the fish counter to have it cleaned.

MAKE AHEAD TIP: Prepare through Step 1. Cover and refrigerate for up to 1 day. Reheat and proceed with Step 2.