Cacio e Pepe

3 tablespoons butter divided
Lots of freshly cracked black pepper
1 cup freshly grated Reggiano parmesan cheese
1/2 pound spaghetti

This sauce is made while the pasta is boiling.
Boil the spaghetti in highly salted water for one minute less than package instructions.  While the pasta is cooking, melt two tablespoons of butter over medium heat in a saute pan large enough to hold the pasta.  Add the black pepper and cook, swirling the pan, for about a minute.  Before draining the pasta, scoop out one cup of the pasta water.  Add 1/2 cup of the pasta water to the pan with the butter and bring to a boil.  Add the pasta to the pan along with the remaining tablespoon of butter and the parmesan cheese.  Toss to combine, adding additional pasta water if the sauce gets too dry.