Put all other ingredients, including the spinach, in a blender and chop until you get a creamy sauce. Then bring to the boil in a saucepan and immediately return to the boil over the lowest flame or heat for 10 minutes. If the sauce gets too thick, add the cream. If necessary, season with parmesan, salt and pepper.
This sauce is intended for ravioli, tagliatelle or casseroles. For casseroles, you can add the sauce directly without boiling it.