Wash the celery leaves in cold water and lightly pat them dry.
Add all the ingredients, except the olive oil, to a food processor bowl. Pulse until a thick paste forms (scrape the ingredients from the sides of the bowl from time to time).
Add the olive oil and pulse the sauce at the lowest speed until well combined or whisk in the olive oil by hand.
Season to taste with salt and pepper. You can also add more olive oil if you want a thinner consistency of your pesto.
Enjoy!
Notes
Storage and freezing: The celery leaf pesto will keep up in the fridge for up to 3 days (stored in a tightly closed container or tightly covered with plastic foil). If you want to keep it longer, pour a small layer of olive oil on top of the pesto. This way you can keep it in the fridge for up to a week. Pesto freezes very well. Freeze it up to 6 months.
Calories = whole recipe. This is only an estimate!