Prepare pasta according to package directions, using a very large pot. Reserve ½ cup of the pasta cooking water. Drain the pasta. Return to the pot and stir in the butter.
Meanwhile, add the ricotta, lemon zest, salt, Parmesan cheese, and ¼ reserved pasta cooking water to the pasta. Stir well to make a creamy sauce.
Add a little more of the reserved pasta water at a time if needed to make a smooth but thick sauce.
(If you want a stronger lemon flavor, add a squeeze of fresh lemon juice.)
Serve immediately topped with optional toppings as you prefer.
