The lessons we learned in Italy on how to make classic basil pesto also apply to nontraditional pestos such as this one. Grind the cheese, don’t grate it. Roughly chop the herbs before processing. Add the ingredients to the processor in stages rather than dump them all in all at once. Use pasta-cooking water to marry the pesto and noodles. In this recipe, Parmesan and walnuts add rich, meaty flavor; sage brings woodsy, earthy notes; parsley brightens with its fresh flavor; and a small amount of ricotta ties everything together with its creaminess.