Bucatini with Walnut-Parsley Pesto

• 1 cup walnuts
• 6 pickled Calabrian chiles or 1 Fresno chile with seeds
• 1 small garlic clove, finely grated
• 1½ ounces Parmesan, finely grated (about 1½ cups)
• ⅓ cup olive oil
• 1 cup chopped fresh parsley, plus more

Kosher salt, freshly ground pepper

• ¾ pound bucatini or spaghetti

1. Preheat oven to 350°. Toast walnuts on a rimmed baking sheet, tossing occasionally, until fragrant and slightly darkened, 8–10 minutes. Let cool.
2. Pulse ¾ cup walnuts in a food processor or blender until very finely chopped (but not pasty). Reserve remaining walnuts for serving. Remove stems from chiles; add to food processor. Pulse until finely chopped. Transfer walnut mixture to a medium bowl and stir in garlic, Parmesan, oil, and 1 cup parsley. Season pesto with salt and pepper.
3. Cook pasta in a large pot of boiling salted water, stirring occasionally, until al dente. Drain, reserving 1 cup pasta cooking liquid. Return pasta to pot and add pesto along with ½ cup pasta cooking liquid. Toss, adding splashes of cooking liquid as needed, until pesto coats pasta and sauce is glossy.
4. Crush reserved walnuts with the flat side of a knife. Divide pasta among bowls and top with walnuts and more parsley.
5. Do Ahead: Pesto can be made 2 days ahead. Cover and chill.