Drain the cashews and combine them with the oil, mustard, turmeric, miso, lemon, salt and pepper in a high-speed blender. Puree until it is fairly smooth.
Slowly add the water to the blender while the blender is running. Continue to puree the mixture until it is silky smooth and creamy.
Taste and adjust the seasoning as needed. The sauce will be very lemony but it will mellow after it is thinned and used to top veggies. Place the mixture in the fridge and use up within 5 days.
To serve, take out as much hollandaise as you need. Place it in a heat-proof bowl and gently warm it over a pot of boiling water. Add some warm water to thin to the desired consistency and continue to stir until warmer. Serve and enjoy!
Notes
You don't want to heat the hollandaise in a pot over direct heat as it will cook the cashews.