Fill a large pot with water and bring to a boil over high heat. Add a couple tablespoons of salt and the pasta and cook until al dente. Reserve a cup of the pasta cooking water. Drain the pasta and return to the pot.
With the heat on low, toss the pasta with 1/2 cup of the grated Parm, cream, butter and parsley, tossing constantly. If the pasta seems dry, add some of the reserved cooking water. Off the heat, toss in the remaining parm.