Put a large pot, filled with water, on high heat. While the water is heating up, melt the butter in a skillet over very gentle heat, making sure that the butter just melts without coloring at all. Turn off the heat.

When the water comes to a boil, add a good pinch of salt and the noodles. Cook only until quite al dente, typically 2-3 minutes for store-bought fettuccine, a bit less for the freshly made kind.

Now drain and transfer the fettuccine to the skillet. Add a pinch of salt and mix vigorously with a fork and spoon, or with some long tongs. Add a handful of cheese and a ladleful of the pasta water and mix again, then more cheese and mix, until the cheese has been used up. Add a bit more pasta water if and when needed—the cheese should melt into a smooth, creamy sauce. It should not be at all watery, but the pasta should be 'loose' and slither around the pan easily.

Serve the fettuccine immediately, with additional grated cheese for those who want it. While not part of the original recipe, a fresh grinding of black pepper would not be amiss.