For the sauce: Place a heavy saucepan over medium heat. When hot, add the oil and butter. When the butter is melted, add the fennel, carrot, celery, leeks, onions and bell pepper. Cook, stirring, until tender, about 5 minutes. Add the tomatoes, 2 cups water, salt, tomato paste, basil, oregano, pepper, thyme, bay leaves and cayenne. Simmer, stirring frequently, until reduced and thickened, at least 2 hours and up to 4 hours.
For the seafood: Scrub the clams well, place in a large saucepan and pour in about 1/2-inch water. Place over medium-high heat and steam until the shells open, about 5 minutes. Discard any clams that do not open.
Dust the halibut, swordfish, shrimp, crabmeat, prawns and scallops with flour. Heat the oil and butter in a large skillet over medium heat. Saute the seafood until golden, in 2 batches if necessary, 4 to 7 minutes. Add the wine and cook, stirring, until reduced slightly, about 1 minute.
Add the sauce, stir well, cover the pot and cook over low heat until heated through, about 7 minutes. Pour into a serving dish, place the clams on top and sprinkle with parsley. Serve immediately.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.