Put all ingredients, except the cilantro, into a blender and blend on high until nice a smooth.
Add cilantro and pulse until chopped but not pureed in.
If you are not using a high speed blender, you can grind the dry cashews into a fine powder using a coffee grinder (do not boil them for this method). You can also soak them overnight or boil them for 30 minutes.
Sauce thickens in the fridge, allow to cool a bit before serving.