In a food processor (see note), combine basil, nuts, and parmesan.
Blend until smooth.
Gradually add oil, pulsing and checking consistency frequently. It should be about the consistency of a smoothie. Don't add it all at once, you may not need it all.
Add salt to taste - I usually add a little less than I normally would and then make the final seasoning alterations when it is combined in whatever I'm serving it with (pasta, sauce, etc).
Serve a few tablespoons over warm pasta (see note) or freeze in ice cube trays for later use. It also makes a great addition to sandwich spreads, creamy sauces, or bread!
• Almost any mild flavored, raw nut will work in this recipe. I use pecans most often but walnuts, pine nuts, and sunflower seeds also work well. • I have also used an immersion blender to blend pesto and it works fine. • The consistency of pesto can be altered in a pasta dish by using pasta water. • I like to use pesto sparingly, so I would serve only half of this recipe over 1 pound of pasta. Experiment to see what taste you prefer!