Drain and rinse the soaked cashews thoroughly. If you boiled them, be careful as they will be hot.
Place the drained cashews into a blender or the cup of an immersion blender. Add the water, fresh lemon juice, nutritional yeast, apple cider vinegar, Dijon mustard, minced garlic (or garlic powder), salt, and pepper.
Blend on high speed until the mixture is completely smooth and creamy. This may take a minute or two, depending on your blender. If using an immersion blender, blend until no cashew pieces remain and the dressing is silky smooth. Scrape down the sides as needed.
Check the consistency. If the dressing is too thick for your liking, add more water, one tablespoon at a time, blending after each addition until you reach your desired pourable texture.
Taste and adjust seasonings. You might want a little more salt, pepper, or lemon juice to suit your preference.
Transfer the dressing to an airtight container or jar.