Saffron gives this simple Sardinian ragu lots of character. The spice’s unique, vaguely floral, slightly minerally flavor pairs beautifully with the sausage, tomatoes and salty pecorino, but since saffron is a somewhat rarified ingredient, we’ve kept it optional. Even without, the dish is delicious. Our favorite pasta for this recipe is orecchiette, a coin-sized, saucer-shaped noodle that does an excellent job of catching the bits of sausage. Small shells and campanelle work well, too. If you can find pecorino Sardo, a sheep's milk cheese from Sardinia, use it in place of pecorino Romano; it has a milder, slightly smoky flavor and adds complexity to the dish.