2ouncesspaghettior your favorite pasta shape. Two ounces of spaghetti is about the diameter of a quarter when gathered together. If using short pasta like penne or ziti, measure about ⅔ cup to equal 2 ounces.
1 ½tablespoonspesto(use store-bought pesto or homemade pesto)
1 to 2tablespoonsreserved pasta water
2tablespoonsfreshly shredded Parmesan cheese-plus more for topping
Bring a medium pot of water to a rolling boil. Add the pasta and cook until al dente according to the package directions. Before draining, reserve ¼ cup of the pasta water. Drain and transfer the pasta to a bowl.
Stir in the pesto and 1 to 2 tablespoons of the reserved pasta water. Toss until evenly coated, adding a little more water if the sauce is too thick.
Stir in 2 tablespoons of grated Parmesan. Taste and add salt if needed.
Sprinkle with the remaining tablespoon of Parmesan and serve immediately.
Notes
Cook Pasta Al Dente: Slightly firm pasta holds the pesto sauce better and prevents a mushy texture.
Save the Pasta Water: The starchy pasta water helps loosen the sauce and makes it cling to the pasta.
Do Not Heat the Pesto: Toss pesto with hot pasta off the heat. Direct heat can dull the fresh basil flavor and darken the sauce.
Use Freshly Grated Parmesan: Fresh cheese melts more smoothly and gives better flavor than pre-shredded varieties.
Adjust the Sauce: If the pesto feels thick, add a splash of pasta water or olive oil until smooth and glossy.