Place the basil leaves, Parmesan cheese, pine nuts, garlic, salt, and black pepper in a food processor or blender.
Pulse the ingredients a few times until roughly chopped.
With the food processor or blender running, slowly drizzle in the olive oil until the mixture forms a smooth and creamy paste.
Taste the pesto and adjust the seasoning as needed. If the pesto is too thick, you can add a little bit of water or extra olive oil to thin it out.
Transfer the pesto to a jar or other airtight container and store in the refrigerator until ready to use.