If using fresh clams, wash and scrub the clams. Discard those that stay open when handled. Put them in a pan broad enough so that the clams don't need to be piled up more than 3 deep, cover the pan, and turn on the heat to high. Check the clams frequently, turning them over, and remove them from the pan as they open their shells. When all the clams have opened up, detach their meat from the shells, and gently swish each clam in its own juices in the pan to rinse off any sand. Unless they are exceptionally small, cut them up in 2 or even 3 pieces. Put them aside in a small bowl. Line a strainer with paper towels, and filter the clam juices in the pan through the paper into a bowl. Spoon some of the filtered juice over the clam meat to keep it moist. Put the olive oil and garlic in a saucepan, turn on the heat to medium, and cook until the garlic has become colored a pale gold. Add the parsley, stir once or twice, then add the cut up tomatoes, their juice, the chopped anchovy, and the canned or filtered clam juices. Stir thoroughly for a minute or two, then adjust heat to cook at a gentle, but steady simmer for 25 minutes, or until the oil floats free from the tomatoes. Add the clams in the last two minutes if using canned clams. Ahead-of time note: The sauce may be prepared several hours in advance up to this point. Reheat gently when preparing to toss it with pasta. Taste and correct for salt, add the chopped chili pepper, stir two or three times, then remove the pan from heat. Add the cut-up clams (if using fresh clams), stirring them into the sauce to coat them well. Toss thoroughly with cooked, drained spaghettini or spaghetti. Drizzle a few drops of raw olive oil over the pasta and serve at once.