Spaghetti with Clams in Their Shells

In Rome, most “vongole veraci,” characterized by variegated shells about 1 1/2 inches wide and by two little “horns” (siphons), are actually farmed Japanese littleneck clams rather than the prized, and increasingly rare, native species. They are most commonly used in spaghetti alle vongole, part of the pantheon of Roman pastas—carbonara, cacio e pepe and gricia are others—whose sauces are created directly on the cooked pasta. That means the dish is easy to put together but hard to fake: timing, temperature, an experienced hand and, especially, undivided attention make all the difference.