Soak the cashews in enough filtered water to completely cover them. Soak them for at least one hour. If you don't have a high-speed blender, soak them overnight.

Drain the soaked cashews and put them into your blender with the juice from the lemon and the salt. Blend, stopping to scrape down the sides as needed. (Use the tamper if you have a Vitamix.) The mixture should end up a very smooth sour cream consistency. If you need to, add a little bit of filtered water to get it to blend.