How to Make It
Bring a large pot of salted water to a boil over medium-high. Add green beans, and cook until just cooked through and tender, about 2 minutes and 30 seconds. Using a spider, transfer beans to a colander, and set aside. Return water to a boil over medium-high, and add pasta. Cook, stirring often, until al dente, about 10 minutes. Reserve 1 cup cooking liquid; pour pasta and remaining cooking liquid into colander over beans. (This will warm the beans if they have begun to cool.)
Combine parsley, basil, olive oil, garlic, salt, and cayenne in a food processor or blender, and pulse until pureed but still slightly chunky, 8 to 10 times. Transfer to a warmed serving bowl. Stir in pecorino Romano, and set aside.
Transfer pasta and beans to serving bowl with pesto, and toss to combine. Add some of the reserved cooking liquid, 1 tablespoon at a time, to loosen pesto, ensuring pesto evenly coats pasta mixture. Serve immediately, passing extra pecorino Romano at the table.
Regular green beans are thicker than French haricots verts, but haricots verts may be substituted.