Pesto is a gift from summer—a nutty, herby distillation of a sweet-smelling, sunshine-loving herb. But fall doesn't have to mean giving it up altogether. The classic basil version is just one interpretation of an open-ended technique: The word "pesto" has its roots in the Italian word for "pestle," and it means the technique of using a mortar and pestle (or more often nowadays, a food processor) to make a flavorful paste combining garlic, nuts and oil with vegetables or herbs. In pesto's birthplace, ingredients like parsley, mint and olives commonly end up in the mix. Fall, especially now when...