Add tiger nuts into a small bowl and add cover in water ½ litre of water (just over 2cups)
Soakt hem overnight or longer, but at least for 8 hours.
In a clean jug, add black tea leaves with the rest of the water. Water should be lukewarm. Let it cold-brew in the fridge overnight too. You can do this and previous step at the same time.
Once the tea is brewed and tiger nuts absorbed water, prepare a blender and a clean cheesecloth.
Strain the water from tiger nuts and discard it.
Strain the tea. Do not discard it.
Add tiger nuts to a blender (in one batch if you have a bigger blender or divide into 2-3 parts with 2-3 parts of cold-brewed tea). Blend well.
Use a cheesecloth to strain the horchata tea milk into a clean glass or jug. You may need to repeat this step once or twice if you want a cleaner drink.
Add sweetener if needed and serve or store in the fridge.