This is a Catalan classic, a simplified paella whose success depends entirely on the quality of the fish stock. "A banda" means apart, and refers to the way the dish is traditionally served, with the rice as a first course and the fish as a second course. But I like to serve them together as a main dish. The dish is also traditionally served with allioli, a strong garlic mayonnaise.
For the broth: In a lidded pot, combine the clams with 1/4 cup water, 1/4 cup wine, and 1 tablespoon onion. Turn heat to medium high, cover and cook 6 minutes, or until all the clams have opened. Remove clams from shells, rinse and set aside. Strain broth through a fine-mesh strainer lined with cheesecloth and set aside.
In a large pot, combine the shrimp shells and heads with the clam broth, remaining onion, garlic cloves, remaining wine, bouquet garni and the soup fish or heads, tails and bones. Cover with water-2 to 4 quarts. Bring to boil, reduce heat to low and simmer 2 hours. Strain through a fine-mesh strainer lined with cheesecloth. Measure out 7 cups (freeze extra).
For the rice: Pound together the 2 whole garlic cloves, cayenne, saffron, paprika and salt in a mortar and pestle. Scrape into a 2-cup measuring cup and blend with 1 cup of fish broth. Set aside.
Heat 3 tablespoons olive oil in a large nonstick skillet or paella pan over medium heat and add the crushed garlic and chile peppers. When they turn light brown, remove them from the pan and discard. Add the rice and cook, stirring, until the grains are coated with oil, 3 to 4 minutes. Stir in the diluted garlic and cayenne mixture, then add 5 cups fish stock, bring to a boil, reduce the heat and cook without stirring, uncovered, for 30 minutes, or until there is no longer liquid in the pan. Remove from the heat, cover and let sit for 15 minutes.
For the fish: While the rice is cooking, cook the fish and shrimp. Heat olive oil in large nonstick frying pan and add the minced onion. Cook until it begins to soften and add the garlic, tomato, and parsley. Cook, stirring, until the mixture is soft and fragrant, about 5 to 10 minutes. Add the fish fillets and steaks, turn to coat all sides, then add 1 cup of fish broth and bring to a simmer. Cook 5 to 8 minutes, or until the fish is cooked through. Remove the fish from the pan and set on a serving platter with the clams. Cover with foil to keep warm. Add the shrimp to the broth, cook 2 to 3 minutes, until pink and opaque, and remove from the pan. Pour the mixture in the pan over the fish and shellfish.
Serve the rice first and then the fish, or serve together, with garlic mayonnaise if you wish.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.