How to Make It
Heat oven to 350°F. Spread the walnuts on a rimmed baking sheet and toast, tossing occasionally, until fragrant, 6 to 8 minutes; let cool. Chop 2 tablespoons of the walnuts and set aside.
Meanwhile, bring a large pot of salted water to a boil. Add the kale and cook until bright green, 30 seconds. Transfer the kale to a colander (reserve the cooking water); squeeze dry when cool enough to handle.
In a food processor, combine the kale, pecorino, garlic, the remaining ⅓ cup of unchopped walnuts, ½ teaspoon salt, and ¼ teaspoon pepper. Process until finely chopped. With the machine running, add the oil through the feed tube in a steady stream.
Bring the reserved cooking water to a boil and cook the pasta according to the package directions. Reserve ½ cup of the cooking water; drain the pasta and return it to the pot. Add the pesto and ¼ cup of the reserved cooking water and toss to coat (add more cooking water if the pasta seems dry). Serve the pasta sprinkled with the pecorino and chopped walnuts.