Prepare the tomato sauce 30 minutes before the clams are to be cooked. Preheat the oven to 500ºF. Bring a large, deep pot of salted water to a rolling boil. Meanwhile, open the clams with a clam knife and reserve the liquid. There should be about 1 cup of liquid and about 3/4 cup of clams. Chop the clams coarsely. Drop the spaghetti into the boiling water and cook for exactly 5 minutes. Drain immediately. Transfer the spaghetti to a large baking dish and add the simmering sauce and the clam juice. Sprinkle the chopped clams on top. Cover the dish with aluminum foil and seal tightly. Bake for 10 minutes. Remove the foil and transfer the contents of the dish to a hot platter or soup bowls and serve. Serve with grated Parmesan cheese, if desired. Makes 6 servings