Cook sweet potato. Put it in a bowl when it's cooked and mash it.
Add dark chocolate to sweet potato while it's still warm and let it melt.
When it melts add all the other ingredients and mix everything together.
Put it in the fridge for at least one hour, so it can harden a bit.
Then make balls and cover them with dark chocolate.
Sprinkle some chopped pistachio on top and place in the fridge until chocolate hardens completely.