Before you proceed with the recipe, sterilize all your kitchen equipment. I like to use a dishwasher, but regular soap and hot water work just fine.
Add soaked (or boiled) cashews into a high-speed blender. Start the blender and add water slowly, until the cashews are blending smoothly and turning into a thick cream. Depending on how hydrated your cashews are, you might need a little more or little less water than 1 cup.
Transfer the cashew cream into a glass bowl. Add the probiotic capsule and stir with a wooden spoon (avoid using metal utensils as metal can react with the probiotics). Add the salt and stir again.
Cover the bowl with a piece of cheesecloth (or an airtight lid for a quicker culturing). Place the sour cream in oven for about 24-48 hours. (The culturing time will depend on many factors, such as the temperature in the oven, the temperature in the house, if you're using an airtight lid, how tangy you like your sour cream, etc).
Stir the sour cream after 24 hours and taste. If it's not tangy enough, cover it, and put it back in the oven. I usually leave my sour cream in the oven for about 36 hours at 80°F (27°C).
If the sour cream isn't tangy/sour enough for your taste, add some lemon juice.
Transfer the sour cream into a glass jar with an airtight lid. Put it in the refrigerator for 6 hours to chill. The sour cream will continue to thicken in the refrigerator. You can always add a splash of water and give it a stir for a thinner consistency.
Store leftover sour cream in an airtight container in the refrigerator for up to 5 days.
For longer term storage, freeze in an airtight container for up to 3 months.
*Soak the cashews in water for at least 8 hours (or overnight) so they soften up and are easy to blend. When the cashews are done soaking, drain the water and rinse the cashews thoroughly. If you're using truly raw cashews, you might want to boil them for 1-2 minutes to kill any pathogenic bacteria.
**If possible, choose probiotic capsules that offer several strains of Lactobacillus bacteria, as well as beneficial Streptococcus thermophilus and Bifidobacterium strains. This will create a more complex sour cream flavor than using Lactobacillus acidophilus alone.
***You can add lemon juice for more sour flavor.
****Prep time does not include soaking the cashews (8 hours).