A high-speed blender is recommended for the creamiest consistency; if using a standard blender, soak cashews first by placing them in a bowl and covering with boiling water. Soak for 1 hour, then drain. Alternatively, substitute 6 tablespoons raw cashew butter (a very full ⅓ cup).
For the ingredients where a range is indicated, begin with the lesser amount. Combine all ingredients in a blender, and blend until smooth, stopping to scrape down the sides as needed. Taste and adjust acid, salt, and sweetness.
Use immediately or transfer the mayo to a jar and refrigerate until chilled, 2 to 4 hours. It will thicken as it cools.