Soak the cashews in water for at least 2 hours, up to 8 hours. If soaking over night, be sure to refrigerate.
Drain and rinse the cashews. Add to the food processor with chicken broth, nutritional yeast, and garlic. Blend until smooth and creamy.
Halve and zest the lemons. Add the juice of both lemons plus the zest to the cashew sauce along with the mustard. Pulse for a few more seconds until combined. (Keep refrigerated, good for 7-10 days.)