Christopher Kimball’s Milk Street

Basil is pesto’s essence and also its liability. Peppery arugula, lemon juice and a slick of oil keep this one bright green for days.

Basil pesto has an annoying habit of turning army-green because of oxidation. Blanching the basil is one solution, but it’s not only a nuisance, it dulls the herb’s flavor. Our solution: add some arugula, which better holds its color and also adds a pepperiness that complements the other ingredients. And for added insurance, we include a little lemon juice to slow down the oxidation. (If you don’t have a lemon on hand, just leave it out.) Short pasta with twists or curls—such as gemelli, casarecce, cavatappi or fusilli—is a perfect match for a thick, smooth sauce like pesto. If you’ve made the pesto in advance, transfer to a small container, spread into an even layer, pour on just enough olive oil to cover the surface to limit air exposure and refrigerate for up to three days.

Don’t over-process the pesto. Once the basil and arugula are added, pulse in 1- to 2-second bursts and scrape the bowl often. If you run the processor continuously, the pesto turns into a lifeless puree. When saucing the pasta, don’t add more than ¼ cup cooking water or pesto will taste dilute.