Wash and soak the Idli and Njavara rices in water for about 5 to 6 hours. Also soak the lentils and fenugreek seeds for 3 hours. Drain the rices and lentils completely and discard the water.
Wash the rice flakes. Grind the rice with the beaten rice flakes, if using, and enough water till smooth. Do not add too much water as the final batter should be somewhat like thick pancake batter in consistency. Transfer to a large container, large enough to let the total batter rise to almost double volume.
Also grind the lentils and fenugreek seeds with water till smooth and fluffy but not watery. Transfer to the container with the rice batter. Using your hand, mix together till well blended. Cover loosely and let it rise overnight or at least 8 hours. It will ferment, rise till almost double in volume and develop a slight tang.
Once the batter has fermented, add salt to taste. Mix well. Make Khotte or little baskets out of the Jackfruit leaves. Stitch together the tips of four leaves using the coconut leaf stick pieces. Then pull one leaf up with the stalk end pointing upwards. Pull the leaf next to it also upwards and join the edges together and stitch with one or two stick pieces. Repeat with the other two leaves forming a small basket or cup. Make as many baskets as requires. Two Kadubu should suffice per person. See the video link above in the text for a better idea on how to fashion the leaf baskets/ cups.
Pour batter to fill 2/3rd of each Khotto or basket. Carefully arrange the baskets in a small tray or steamer pan. Ensure the water is boiling when you put the Kadubu batter for steaming. Steam cook for about 15 minutes till done. The surface of the Kadubu or rice cakes will be set and not sticky. A knife or skewer pushed in the middle should come out clean. Let it cool a bit. Serve with Chutney and/ or Sambhar. Note the leaves are to be unwrapped and discarded.