Spaghetti with walnut and chili pesto
1 cup walnuts
1 jalapeno, seeds removed
1 small garlic clove, finely chopped
1½ ounces Parmesan, finely grated (about 1½ cups)
? cup olive oil
1 cup chopped fresh parsley, plus ¼ cup chopped and reserved
Kosher salt, freshly ground pepper
¾ pound spaghetti
Preheat oven to 350°. Toast walnuts on a rimmed baking sheet, tossing occasionally, until fragrant and slightly darkened, 8–10 minutes. Let cool.
Pulse ¾ cup walnuts in a food processor or blender until very finely chopped, but not to a paste. Reserve remaining walnuts for garnish. Remove stems from jalapenos, and seeds; 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.
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.
Crush reserved walnuts with the flat side of a knife. Divide pasta among bowls and top with walnuts and more parsley.