Step 1

In a large pot, bring 3 quarts water to a boil. Add the pasta and 2 teaspoons salt, then cook, stirring occasionally, until the pasta is just shy of al dente. Reserve 1½ cups of the cooking water, then drain and set aside; reserve the pot.

Step 2

Meanwhile, in a 12-inch nonstick skillet over medium, combine 2 tablespoons oil and the garlic. Cook, stirring occasionally, until the garlic is golden brown, about 2 minutes. Remove and discard the garlic. Increase to medium-high and heat the oil until shimmering. Add half the zucchini and a pinch of salt; cook, stirring occasionally, until golden brown all over, about 5 minutes. Transfer to a small bowl. Using the remaining 1 tablespoon oil cook the remaining zucchini in the same way. Transfer to the bowl and set aside.

Step 3

In the large pot over medium, combine the butter, pepper flakes and ¼ teaspoon salt; cook, stirring, until the butter melts. Add the pasta and reserved cooking water; cook, stirring to combine, until the pasta is al dente and lightly sauced, 2 to 3 minutes.

Step 4

Off heat, add the cheese, stirring until melted and creamy. Add about two-thirds of the basil, the pistachios and the zucchini; toss to combine. Taste and season with salt and black pepper. Serve sprinkled with the remaining basil.