Bring a large pot of water to a boil while making the sauce.
Melt 2 tablespoons of the butter in a skillet and add the spinach. Season with salt and pepper and cook until wilted and tender.
Stir in the cream and simmer for about 5 minutes. Remove from heat while cooking the pasta.
Add a generous amount of salt to the boiling water, then cook the pasta to al dente according to the package directions.
Put the rest of the butter in a large mixing bowl, plus a tablespoon or two of the hot pasta water.
Drain the pasta and add to the bowl along with half the Parmesan and the spinach mixture.
Taste for seasonings and add more salt and pepper if desired. Add a few gratings of freshly ground nutmeg, too.
Stir together and serve with the remaining Parmesan.
