Bring a large pot of water to a boil, and salt it. Cook the pasta until it is tender but just short of the point at which you want to eat it.
Meanwhile, place butter and olive oil in a saucepan large enough to hold the cooked pasta; turn the heat to medium and add the sage. Cook until the butter and oil begin to brown and the sage shrivels.Turn heat down to low.
When pasta is almost done, scoop out a cupful of the cooking water and set aside. Drain the pasta, immediately add it to the sage mixture, and raise the heat to medium.
Add 1/2 cup of the reserved water, and stir. Cook about 30 seconds or until some of the water is absorbed and the pasta is perfectly done.
Stir in the cheese until the sauce becomes creamy. Thin it with a little water if necessary.