Soaking is required if you are using a regular blender or food processor. It's not required but recommended if you have a high-speed blender like Vitamix.Soak the cashews with hot water forabout 1 hour.
Drain and rinse the soaked nuts and add them to the blender with water, lemon juice, apple cider vinegar, and salt.
Blend at high speed until silky smooth. It might take from 3 to 7 minutes. Add more water if you want thinner sour cream.
You can use the vegan sour cream immediately, although still slightly warm from the blending. Or store it in the fridge for up to 5 days in an airtight container. It will thicken up as it cools down, becoming easier to spoon. If you want to make it thinner, add water.You can add some finely chopped dill or chives on top.