Melt the butter in a high pan over low heat, being careful not to burn it. Put the pasta in a saucepan with salted water and cook until al dente, then drain, but do not throw away the water!
Add a little pasta water to the butter, about 10 tablespoons. Boil the whole thing until it is creamy. Turn off the stove and slice in the truffle with the truffle slicer, stir and make sure that it no longer boils.
Mix, then stir in the pasta and arrange on a plate.