If you do not have a high-speed blender, soak the cashews for at least 4 hours, drain and rinse them until the water runs clear.
Place all ingredients in a blender. Blend until the mixture is smooth and creamy, stopping to scrape down the sides as necessary. If you’re having trouble blending the mixture, or would prefer a thinner consistency, slowly blend in up to ½ cup additional water, as needed.
Taste. If you want more tang, add extra lemon juice (1 tsp at a time). If you need a more intense flavor, add a little more salt.
Serve immediately or chill the sour cream for later.
Leftovers keep well, chilled, for about 5 days. The sour cream will thicken up a bit more as it rests; you can thin it by whisking in a small amount of water later, if necessary.
