About 1cup freshly grated Parmigiano-Reggiano cheese, plus more for serving
Salt and freshly ground black pepper
Instructions
Bring a large pot of water to a boil and salt it. Cook the pasta until it is tender, but a little short of the point at which you want to eat it.
Meanwhile, put the butter in a skillet or saucepan large enough to hold the cooked pasta; turn the heat to medium and add the sage. Cook until the butter turns nut-brown and the sage shrivels, then turn the heat down to a minimum.
When the pasta is just about done, scoop out a cupful of the cooking water. Drain the pasta, immediately add it to the butter-sage mixture, and raise the heat to medium. Add 1⁄2 cup of the water and stir; the mixture will be loose and a little soupy. Cook for about 30 seconds, or until some of the water is absorbed and the pasta is perfectly done.
Stir in the cheese; the sauce will become creamy. Thin it with a little more pasta water if necessary, season liberally with salt and pepper to taste, and serve immediately, passing more cheese at the table if you like.