Boil the pasta in salted water according to the directions on the package.
Add the spinach and fry about 5 min. until the spinach darkens. Season with salt and black pepper. Add the cream and mascarpone and stir well.
If the sauce is too thick, you can add a ladle of the water the tagliatelle are boiling in. Strain the boiled pasta and add it to the sauce. Stir well and sprinkle with parmesan.