Prepare basil - pick only green leaves and cut off the stems.
Mix parmesan and pecorino. You can also use only one type of cheese (1/2 cup).
Mix all the ingredients in a blender and chop. Make sure the structure is not too fine and not too smooth, pesto shouldn't be pureed. Add as much olive oil as needed to give pesto the consistency you prefer.
Ready to serve! Pesto is a great dressing that can be used on salads, pastas, pizzas, chicken, soups or even as a crostini topping.
Your homemade pesto can be stored in a closed container in refrigerator for up to a week.