1. Firstly, in a large bowl soak 1 cup idli rice, 1 cup raw rice and ¼ tsp methi seeds / fenugreek seeds for 5 hours.
2. In another bowl soak 1 cup urad dal / black gram skinned for 5 hours.
3. After 5 hours, drain off the water and transfer the urad dal into the blender or grinder. blend to smooth and fluffy batter adding water as required. transfer the urad dal batter to a large bowl.
4. Drain off the soaked rice into the blender. blend to a coarse batter (consistency like of rava) adding water as required. transfer the rice batter to the same mixing bowl.
5. Mix well making sure rice batter and urad dal batter is combined well.
6. Cover and ferment in warm place for 8 hours or until the batter doubles.
7. Next day, mix the batter gently without disturbing the air pockets. keep aside.
8. In a small kadai, heat 2 tbsp gingelly oil and splutter ½ tsp cumin seeds, 1 tsp crushed pepper, a pinch hing / asafoetida, 5 chopped cashew nuts and few curry leaves.
9. Pour the tempering over the idli batter.
10. Also, add ½ tsp ginger powder and 1 tsp salt. mix gently making sure the batter is well combined.
11. Now heat the banana leaf slightly to make it flexible. you can alternatively use mantharai leaf cups.
12. Fold slightly and place in a small cup. grease the cup with gingelly oil.
13. Pour in prepared kanchipuram idli batter into the cups filling it to 3/4th.
14. Place the cups into the steamer and steam for 20 minutes.
15. Finally, enjoy kanchipuram idli with chutney and sambar.