1/ 4 teaspoon hot red pepper flakes, or more to taste
31/ 2 tablespoons finely chopped parsley
Freshly ground black pepper
Scrub the clams and then rinse 2 or 3 times in cold water. Fill the sink with cold water and add 2 small fistfuls of coarse salt. Put the clams in a colander and immerse them in the water. Sprinkle a handful of cornmeal over the clams, cover the colander with a lid, and leave for at least 5 hours, or better, overnight, in the refrigerator. When ready to use the clams, rinse them 3 times in cold water and drain.
In a large skillet, heat 2 tablespoons of the olive oil over high heat. Add the clams. Cover the skillet with a lid and cook, shaking the pan continuously, until the clams open, 3 or 5 minutes.
Let the clams cool a little. Set aside a few of the clams in their shells to serve on top of the pasta. Strain the clam juice in the skillet through a single thickness of paper towel and reserve 2/ 3 cup of the juices. Shell the remaining clams and add them to the reserved juice.
In a large pot of boiling salted water, cook the spaghetti until it is very al dente.
While the pasta is cooking, heat the rest of the oil in a clean large skillet over moderately low heat. Add the garlic and cook slowly until light brown, 3 to 4 minutes. Quickly add the hot pepper, the clams with their juice, and 2 tablespoons of the parsley. Simmer for 1 to 2 minutes to heat through. Season with salt and pepper to taste.
Drain the pasta and add it to the clam sauce in the skillet. Toss rapidly and thoroughly over moderate heat. Transfer to a warm serving dish, arrange the reserved clams in their shells over the pasta, and sprinkle the remaining chopped parsley on top. Serve at once.