Blend all of your ingredients (with the exception of those last 3 tablespoons of olive oil) in a food processor, pulsing as needed to ensure a smooth creamy texture.
Pour into a jar before pouring the final 3 tablespoons of oil on top.
Seal with an airtight lid and refrigerate; it will readily keep a week or two in the refrigerator as long as well-sealed.
After each use, place a thin layer of olive oil back on top of the pesto before re-refrigerating to help it last.