"This is a favorite because it combines two white cheeses and cream and very little else. The walnuts add crunch and the chives bring extra flavor. Topped with grated Parmesan, it needs nothing more except a green salad or vegetable."
Bring a large pan of salted water to the boil. Add pasta, reduce heat to medium and cook 12 minutes or according to package directions.
Meanwhile, in a large heated serving bowl, combine the ricotta, the mascarpone or cream cheese, the cream, and a small amount of salt (the Parmesan adds salt, so be careful here), and plenty of freshly ground pepper to taste.
Drain ziti, reserving 1 cup of cooking water and add to sauce. Toss coat it well, adding small amounts of pasta cooking water to bring sauce to medium consistency. Add egg yolk, chopped walnuts and chives, and toss again. Top with grated Parmesan cheese, toss lightly and serve.