The main ingredient in traditional pesto sauce is basil. This aromatic herb provides pesto with its distinctive flavor and vibrant green color. Traditional pesto is a blend of fresh basil leaves, garlic, pine nuts, Parmesan cheese, and olive oil. The ingredients are typically crushed together using a mortar and pestle, although modern recipes often use blenders or food processors for convenience. Pesto is popular in Italian cuisine and can be used as a sauce for pasta, a spread, or a drizzle on various dishes.