Step 1

Position a rack in the middle of the oven and preheat to 350 degrees. Arrange the pecans in a single layer on a small sheet pan and toast in the oven for 8 to 10 minutes, stirring halfway through, or until fragrant and slightly darkened. (Alternatively, toast the nuts, stirring frequently, in a dry skillet over medium heat for 3 to 5 minutes.) Transfer to a plate or bowl to cool slightly.

Step 2

Bring a large pot of water to a boil, then salt the water to taste. Add the pasta and cook according to the package instructions until al dente. Reserve about 1 cup of the pasta water, then drain. Return the pasta to the pot.

Step 3

While the pasta cooks, combine the pecans and garlic in a food processor and pulse until the nuts are finely chopped. Add the basil, half of the spinach and half of the oil (it’s okay to eyeball these), the lemon juice, a generous grind of black pepper, and 1/2 teaspoon to 1 teaspoon salt, to taste. Process until pureed, scraping down the bowl as needed. Add the remaining spinach, turn the food processor back on and gradually stream in the remaining oil until smooth and thoroughly combined, scraping down the bowl as needed. Taste, and season with more salt, lemon juice and/or pepper, as desired. You should have about 2 cups of pesto.

Step 4

Transfer 1 cup of the pesto to the pot with pasta and gently toss to evenly coat, splashing in the reserved pasta water 1 tablespoon at a time, as needed, to loosen the sauce.

Step 5

Transfer to a large serving bowl or individual plates, season with more salt, and/or garnish with the parmesan, if using, and serve.