Cook your noodles according to package instructions. When they’re done, be sure to reserve a couple cups of pasta water.
While the noodles cook, spread the butter onto the bottom of a large serving bowl and grate your cheese.
When the noodles are done, put the hot, drained noodles into the serving bowl and mix until the butter is melted and evenly distributed onto the noodles. Next, stir in the cheese. Add about one-quarter cup of the hot pasta water and stir.
Add more water, a little at a time, until the cheese is melted and the sauce is the consistency you want.