A spicy sauce that’s perfect tossed with pasta. Be sure to wash your arugula thoroughly, in at least two changes of cold water, to remove any soil and grit, which you definitely don’t want in your pesto.
In The Bowl of a food processor, blend the arugula and garlic until finely chopped. With the machine running, gradually add the oil, processing until well blended. Transfer the pesto to a large bowl, and stir in the Parmesan cheese, ½ teaspoon of salt, and ¼ teaspoon of pepper. Season the pesto with more salt and pepper to taste. (The pesto can be made 2 days ahead. Cover and refrigerate.)