In a high-speed blender, combine the cashews, water, mustard, tomato paste, maple syrup, vinegar, onion powder, and salt. Secure the lid and blend until smooth, about 60 to 90 seconds.
Taste the sauce and make any flavor adjustments, as needed. Then pour it into an airtight container with a lid and store it in the fridge until you're ready to use it. This sauce will thicken when chilled, so you may need to stir a tablespoon of water to help thin it out again. It will keep well in the fridge for up to 1 week.
Notes
Nutrition information is for roughly 2 tablespoons of sauce. This information is automatically calculated and is just an estimate, not a guarantee.Note: This recipe was updated in December 2023 to use simpler pantry ingredients. If you prefer the original version, you can find that here.