Turn the blender on and slowly add the oil until the pesto is the desired consistency.
Use right away, store in the refrigerator for up to two weeks, or freeze for up to 9 months.
To freeze pesto, I like to put a couple tablespoons in each compartment of an ice cube tray. When they are frozen I dump them in a larger container with a lid and store in the freezer. This method makes it easy to just grab the needed amount. The Vitamix with tamper makes this job a snap, but any blender should work!