Quick soak the cashews: Bring a few cups of water to a boil. Add 1 ½ cups cashews to a measuring cup and pour the boiling hot water on top to cover. Let them soak for 5 minutes, or 1 hour if you don't have a high powered blender.
Drain the cashews and add to high powered blender. Now add ¾ cup fresh water, apple cider vinegar, lemon juice and salt. Blend until very smooth.
Pour the cashew mixture into a bowl and stir in the unsweetened yogurt. This is optional, but it brings the sour cream to another level in terms of texture and flavor.
Use immediately, or transfer to a small covered container and refrigerate. It will thicken up as it chills. The sour cream will keep for about a week. You may also freeze this if desired.
