Cook the pasta in a large pan of boiling salted water for 10-12 minutes, until al dente. Meanwhile, put the cream in a saucepan with the butter and a little grated nutmeg and warm through gently. Stir in the parmesan.
Drain the pasta, reserving about three tablespoons of the cooking water, then tip it straight into the cream sauce. Add as much of the reserved water as needed to loosen the consistency of the sauce to your liking. Mix gently, adding plenty of freshly ground black pepper. Serve immediately.