Chop finely the onion and heat the oil in a large pot, add the chopped onion and let it brown for a few minutes. Add the peas and cook for about 15 minutes with a lid, until they become tender, if necessary adding the vegetable broth and salt. Transfer the cooked peas in a blender and blend to obtain a velvety cream. Put the cream of peas in the pan and add the ricotta cheese, a handful of chopped parsley and the pepper, mix well and keep warm. Meanwhile, boil salted water and let cook the fettuccine. Drain “al dente” and make them jump quickly into the saucepan with the cream. Serve hot the fettuccine with cream of peas and ricotta cheese with a generous sprinkling of parsley and grated Parmesan cheese.