Boil the Rigatoni in plenty of boiling salted water.
In the meantime, remove the skin from the sausage and cut it with a knife. Sauté it in a pan over medium heat until it is well browned.
Separately, in a cup with hot water, dip the saffron pistils which in a few minutes will release all their flavor and color.
Drain the pasta directly into the pan with the sausage, add the saffron, rosemary (very little) and sauté for another 2 minutes.
With the flame off, add the grated Parmesan cheese and serve