"In your September 1997 issue, page 146, you answered a reader's inquiry about why pesto discolors," says Al Herron of Prescott, Arizona. "You offered a traditional solution, but I believe there is a better one: Mix fresh pesto with yogurt, and the pesto will not turn brown over time as it ordinarily does. (For many years I used the olive-oil-on-top trick with limited success.) I have kept leftover pesto mixed with yogurt in the refrigerator for several days with no discernible change in color or flavor. The proportion can vary — as little as one part yogurt to eight parts pesto, or as much as you like for flavor."

Ingredients

　　2 garlic cloves

　　1/2 teaspoon salt

　　2 cups packed fresh basil leaves

　　1/2 cup walnuts

　　1/3 cup freshly grated Parmesan

　　1/2 cup extra-virgin olive oil

　　1/4 cup plain yogurt

　　Mince garlic and mash to a paste with salt. In a food processor purée garlic paste, basil, walnuts, Parmesan, and oil until smooth. Add yogurt and combine well. Pesto keeps, its surface covered with plastic wrap, chilled, 5 days.