Cook the pasta according to the package directions. Reserving 1/3 cup of the water, drain the pasta, then return it to the pot. In a medium bowl, whisk together the butter, ricotta, and pasta water until a rich, creamy sauce forms. Pour the sauce over the hot pasta. Add the herbs, zest, salt, and pepper and toss.
Tip: Ricotta can vary dramatically in taste and texture. Depending on the brand you use, you may need to add extra pasta water and butter to create a sauce that's sufficiently creamy.