When making this elemental roman pasta, most people focus on the cheese (cacio), with purists arguing for youngish pecorino romano. But the peppercorns (pepe) are also essential to this dish, so it's a great time to try a single-origin variety. Boiling down some reserved pasta-cooking water before mixing with the al dente spaghetti concentrates the starch for an even more luscious sauce. Look for a hard grating cheese made without rennet if you want to keep it truly vegetarian.