You can cook your homemade pesto! You can freeze the herbs mixed with the oil in ice cube trays in the freezer. At the time to serve the pesto, defrost the preparation and add the other ingredients (parmesan, nuts and garlic).
Important: Defrost the frozen herbs by letting them sit at room temperature or in the refirgerator. Avoid defrosting the frozen herbs in the microwave. Pesto is a fresh, uncooked sauce. Microwave use can cook the the mix, and hence spoil the taste.