Heat two cups of water in a saucepan or teakettle till boiling. Pour the water over the dates.. Allow the dates to sit for 15-20 minutes.
Drain the dates, reserving the soak water. Place the dates into a blender with 1 cup of the soak water, the vanilla, the cashew butter, and the salt. Blend on a high speed till the dates are very smooth and resemble a sauce. Add more water if needed. The sauce should be thick but pourable. Serve or store.
Sauce will keep in an airtight container in the fridge for up to 5 days.