Pick , wash and soak the rice. Leave it overnight, next morning grind it to a smooth yet thick batter using about 1 & 1/4 cups water approx. Add water gradually and grind.
Clean the jackfruit arils well, remove the seed. Make a purée of jackfruit using less than 1/4 cup of water. You may not need to add any water for the soft variety.
In a mixing bowl, add ground rice, jackfruit purée, cardamom powder, salt, and jaggery. Mix well to incorporate everything, you can taste little of the batter and adjust sweetness adding more jaggery if required. You can also add some finely chopped jackfruit pieces for additional texture.
Transfer about 2 tablespoons of batter to a greased idli plate, or transfer to the entire batter to a greased 9-inch cake tin.
Heat little water in the idli steamer, bring to a boil, now transfer the idli rack to the steamer, cover with lid and steam for about 10-12 minutes or until a toothpick inserted comes out clean.
Once it's slightly warm, unmould the sandon with the help of a blunt knife, Enjoy these warm for breakfast.