For red clam sauce, add the optional tomatoes. To use canned clams, add four 6 ½-ounce cans chopped or whole clams with their juices to the cooked pasta.
Heat in a large pot over medium-high heat:
Add and cook, stirring, until the onion softens, 3 to 5 minutes:
Increase the heat to high and add:
Cover the pot and cook until the clams open. Pour the clams and broth into a large bowl and let cool slightly. Working over the bowl to catch the juices, shuck the clams; if the clams are sandy, rinse them in the broth as you go. Put the clams in a small bowl, strain the broth, and set aside.
Heat in a large skillet:
Add and cook, stirring, for a few minutes:
Add the broth and simmer until reduced to about 1 cup. Meanwhile, cook in a large pot of boiling salted water:
Stir the clams and any liquid into the skillet and stir in:
Drain the pasta and add to the sauce, tossing to coat. Season to taste with: