Wash the celery leaves and the spinach. Put the first four ingredients in the blender with 2 Tbsp. of Evoo. Blend on low and slowly increase the speed. Add 2 more Tbsp. of Evoo and blend for a few more seconds. If the ingredients don’t blend well, add one tablespoon of water. Taste and adjust for salt. The result should be a smooth, light-green sauce.