Step 1

In a large pot, bring 4 quarts water to a boil. Fill a medium bowl with ice water and set it near the stovetop. To the boiling water, add 1 tablespoon salt and the parsley; cook, stirring, until just wilted, about 15 seconds. Using a slotted spoon or mesh sieve, immediately scoop out the parsley and transfer it to the ice bath. Let stand, stirring once or twice, until fully chilled, about 2 minutes. Reduce the heat under the pot to medium.

Step 2

Remove the parsley from the ice bath and squeeze with your hands until mostly dry. Roughly chop the parsley, then add it to a blender along with the garlic, colatura de alici or anchovy and the oil. Puree on high, scraping the blender jar as needed, until the mixture is smooth and thick, 1 to 2 minutes. If the parsley doesn’t fully break down, while the blender is running, drizzle in cold water 1 teaspoon at a time as needed until the pesto is smooth.

Step 3

Return the water to a boil over medium-high. Add the pasta and cook, stirring occasionally, until al dente. Reserve about ¾ cup of the cooking water, then drain the pasta and return it to the pot. Add the pesto and ½ cup of the reserved pasta water; cook over medium, vigorously tossing and stirring, until the pesto clings to the spaghetti, about 2 minutes. Stir in the lemon zest and juice and toss in more reserved pasta water 1 tablespoon at a time as needed so the spaghetti is well sauced. Remove from the heat, then taste and season with salt and pepper. Serve drizzled with additional oil and sprinkled with additional lemon zest.