The primary ingredient in a classic pesto sauce is basil. This fragrant herb is the foundational component of traditional pesto, lending a fresh and aromatic flavor. The classic recipe typically includes crushed garlic, pine nuts, Parmesan cheese, and olive oil, all blended together to create a thick, green paste. Used as a sauce for pasta, a spread for sandwiches, or a dip, pesto is beloved for its rich taste and versatility. While basil is the signature ingredient, variations exist that replace or supplement the basil with other herbs or greens, such as spinach or arugula.