Add the pine nuts to a dry skillet and turn on medium-low heat. Stir the nuts occasionally and watch them carefully as they tend to burn easily. Once they are a light golden color, remove from the heat and set aside.
Make the Pesto
To a blender or food processor, (or use a mortar and pestle) add the pine nuts, garlic cloves, basil leaves, salt, pepper, and lemon juice (if using). Pulse a several times to start breaking up the basil. Scrape down with a spatula.
Turn on the blender/food processor to a low speed and slowly drizzle in the olive oil in a steady stream (my blender has a hole in the lid for this purpose). Stop the machine and scrape sides of the bowl to get any larger chunks loose and pulse several times until you have a slightly chunky texture (or as smooth as you like), and the olive oil is very well incorporated. It should be thick, but not too thick (see photos in post). Add a little more olive oil if too thick.
Add the parmesan cheese and pulse just a few more times to incorporate the cheese.
Refrigerate immediately in an airtight container if not using right away. Or freeze in an ice cube tray and transfer frozen cubes to a freezer baggie. Use in soups, sauces, and dips.
Notes
Storage Tip:
Pesto can be frozen. You can freeze in an ice cube tray and transfer the frozen pesto cubes to a freezer baggie and add to soups, and other recipes.