Combine the drained cashews, coconut milk, and tapioca starch in a blender. Blend until silky smooth.
Transfer the mixture to a saucepan and bring to a simmer. Remove from the heat and let cool.
Add to a glass bowl (no metal!) and stir in the probiotic with a wood, plastic, or glass utensil.
Cover the bowl with cheesecloth and secure it with a rubber band. Let ferment at room temperature overnight or until desired tanginess is achieved.
