Put the spaghettini in enough boiling salted water form and cook until just tender. In the meantime, pluck the parsley leaves. Remove the peel from the onion. Chop both ingredients.
Sauté the parsley, onion and lemon peel briefly in the warm butter until soft. Add the Noilly white wine or possibly Prat and the juice of one lemon. Make the sauce two to three min. Add the heavy cream. Season the sauce with salt and pepper and cook lightly for another moment.
Drain the spaghettini and drain well. Immediately mix with the hot sauce. Serve with freshly grated Parmesan or Sbrinz cheese.