Bring 4 quarts of water to a boil in a large pot for the fettuccine. While the water is coming to a boil, simmer the cream in a large skillet (at least 12 inches wide) over medium heat until it's thickened slightly and has reduced to approximately 1.5 cups. This will take about 8 minutes. Cover with a lid and keep the cream warm (a very gentle simmer is okay).
Add 1 Tablespoon of salt to the water when it's reached boiling and add the pasta. Cook, stirring often, until it's al dente (following time listed on bag of pasta). Reserve 1/2 cup of the pasta water before draining the pasta. Return drained pasta to the pot.
Whisk the butter, parmesan cheese, and nutmeg to the warmed cream, and season with salt and pepper to taste. Add the sauce to the pasta, tossing to coat. Add the reserved pasta water a little at a time to allow the sauce to cling better to the pasta. Serve right away.