In a food processor, add basil leaves (tightly packed), mint leaves (tightly packed), extra virgin olive oil, walnuts, grated parmesan cheese, garlic cloves (peeled), salt, and black pepper.
Blend until a finely chopped mixture forms.
While the food processor is running, begin drizzling in the remaining 4 tablespoon of extra virgin 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 5 days.