Heat ½ cup of the olive oil, the onion, and garlic in a large frying pan, and cook over medium heat, stirring often, for 3 minutes. Add the fish fillets and cook over low heat for 4 minutes, stirring occasionally. Set aside.

Put the clams and mussels into a large pot with ½ cup of water and the white wine and cook, covered, over medium-high heat until the shells have opened, stirring occasionally.

Remove the mussels and clams from their shells and add to the pan with the fish. Strain the juices from the pan the clams and mussels cooked in through a fine strainer lined with a double layer of cheesecloth into a saucepan. Add 5 cups of water and bring the seafood broth to a boil. Reduce heat to a simmer. Put a ladle into the pan and keep it close to the burner on which you’ll be cooking the risotto.

Heat 4 tablespoons of the olive oil in a heavy-bottomed saucepan and add the rice. Stir constantly for 2 minutes. Ladle in 1 cup of seafood broth and, stirring vigorously and constantly, cook until the liquid has been absorbed. Add another ladleful of broth and stir the rice until the liquid has been absorbed. Add the cooked seafood, shrimp, tomatoes, parsley, cayenne pepper, if you like, and 2 ladlesful of broth to the risotto. Stir and continue adding the broth, ½ cup at a time, stirring until the liquid has been absorbed and the risotto is done. If necessary, add boiling water to the seafood broth and keep it simmering.

Five minutes before the risotto is ready, call everyone to the table.

Season the cooked risotto to taste with salt and pepper and stir in the butter. Turn the risotto into a warmed serving dish or bowl and garnish with the parsley sprigs. Serve at once.