If you don't have a high-speed blender, place the cashews in a bowl and cover with boiling water. Leave them to soak for one hour. Then drain the cashews.
Add the soaked cashews to the blender along with the nutritional yeast, lemon juice, white vinegar, water, turmeric, Dijon mustard, garlic powder, onion powder, black salt and cayenne pepper.
Blend until smooth.
Heat the sauce over a double boiler until warmed through. You can improvise a double boiler by placing the bowl of sauce into a pan with a couple inches of water. The sauce will thicken while heating.