Put the sauce, oil and cream into a broad skillet or sauté pan.
Cook the spaghetti in salted boiling water till al dente, drain, reserve a little of the pasta water.
When the spaghetti is almost cooked, warm the sauce to a simmer, reduce it just barely, tossing in the spaghetti when it comes to a boil. Turn off the heat and toss thoroughly to coat. Add chopped parsley if desired. Taste and correct for salt and pepper.