I’ve been working on my pesto recipe for a few decades but I’ve never been 100 percent satisfied. Sometimes I make it in a mortar, like you’re supposed to, but it seems to discolor more with that method. Sometimes I blanch the basil leaves for a few seconds to keep the color, a trick I learned from Michael Chiarello, who also adds a pinch of ascorbic acid for the same reason. But that always seems a bit like cheating. Recently, perusing a new Italian cookbook, I saw another approach that intrigued me.