A bright, creamy weeknight pasta coated in a silky, no-cook lemon pesto made with cashews, Parmesan, and butter for luscious richness—zesty, vibrant, and ready in 20 minutes.
Bring a large pot of heavily salted water to a boil. Add 1/2 lb dried spaghetti and cook until al dente. Reserve 3/4 cup pasta water, then drain the pasta.
Using a vegetable peeler, remove the thin yellow rind from 1 lemon, avoiding the white pith; set the rinds aside. Halve the lemon and squeeze until you have 1 tablespoon lemon juice; set aside.
In a food processor, combine the lemon rind, 1/4 cup raw cashews, and 1/2 oz finely grated Parmesan. Pulse to a sand-like texture. Add 1 tablespoon lemon juice, 2 tablespoons extra virgin olive oil, 1/4 teaspoon fine sea salt, and 1/8 teaspoon freshly ground black pepper. Pulse, scraping down as needed, until a pesto-like paste forms (not perfectly smooth).
Return the hot drained pasta to the pot off heat. Add 1 tablespoon butter, the lemon pesto, and about 1/3 cup reserved pasta water; toss vigorously to coat. Add more pasta water as needed until the sauce is silky (about 1/2 cup total). Taste and adjust salt if needed.
Divide into bowls and garnish with finely chopped fresh basil and additional Parmesan, if desired.