Lemon, Parsley, and Parmesan plus Pasta

Make the pesto: In a food processor, pulse parsley, garlic, red-pepper flakes, lemon zest, and 1 teaspoon salt until coarsely chopped. With machine running, add oil in a slow, steady stream, processing until blended.

Bring a large pot of salted water to a boil. Cook pasta until al dente. Drain, reserving 1/4 cup pasta water.

Toss pasta with pesto and Parmesan, then with reserved pasta water. Grate more lemon zest over each serving, and season with pepper.