Heat the cream in a pan over low heat but do not let it boil.
Take it off the heat and whisk in the grated Parmesan cheese until melted and smooth. Taste the sauce and add the salt as needed. (Salt is an important ingredient here, so do not skip it.)
To dress the pasta with the cream sauce, add the pasta directly to the pan with the sauce and gently shake the pan to coat the pasta with the sauce. Add up to 1/3 cup of the reserved pasta water to loosen the sauce. Serve immediately.
Read the tips in the post on how to make better pasta dishes.