The easiest way -
Melt a stick of butter in a saucepan, add cooked and well drained pasta to butter in pan, sprinkle 1/4 - 1/2 c. grated Parmesan (I use Pecorino Romano - fresh grated) and pour a bit of cream , half-and-half or whole milk; toss well and serve. (work fast - do not burn the butter)