Add fresh basil leaves (packed), walnuts, garlic cloves (peeled), salt, freshly cracked black pepper, grated parmesan cheese, lemon juice, and extra virgin olive oil to the jar of a food processor.
Blend until a finely chopped mixture forms.
While the food processor is running, begin drizzling the remaining olive oil until a slightly coarse sauce is formed. Add additional olive oil if needed for desired consistency.
Scrape the sides of the jar a few times while blending. Taste test for salt and add more if required. Pesto is ready to use immediately, otherwise, store it in an airtight container in the fridge for up to a week. You may want to cover with a thin layer of olive oil or plastic wrap to prevent oxidation.