1/2 pound dry fettuccine pasta
3-4 tablespoons unsalted butter
2/3 cup finely grated Parmesan cheese
Additionally, for creamy version:
1/2 cup cream
Bring a large pot of salty water to a boil and drop in your fettuccine.
Regular: Melt the butter in a large sauté pan set over low heat. Once the butter has melted, turn the heat off.
Creamy: Melt the butter in a large sauté pan set over low heat. Add the cream to the butter as it melts. Stir often to combine the two, do not turn off the heat, but keep the heat at its lowest setting while the pasta cooks.
When the fettuccine is al dente (cooked, but still a little firm) lift it out of the pot with tongs and move the pasta to the sauté pan. Do not drain the pasta. You want it wet with the cooking water. Turn on the heat under the sauté pan to medium and swirl the pasta and butter together to combine. Add half the cheese, then swirl and toss the pasta until it has incorporated into the sauce. Add the rest of the cheese and repeat.
Serve at once with either a little black pepper (for classic version) or nutmeg (for creamy version) ground over the pasta.