Place basil leaves in a blender.

Add olive oil, garlic, parsley, salt, pepper, and pine nuts (or walnuts or almonds) to the blender.

Blend until finely chopped, pausing to push down ingredients as needed.

If the mixture is too thick, add more olive oil until a loose paste consistency is achieved.

Transfer the pesto from the blender to a bowl.

Stir in the Parmesan cheese.

Serve over pasta, fish, bread, or other dishes.