Measure poha and sooji/rava. Add water to jaggery till it immersed level and melt it. Set the jaggery syrup aside. Keep all other ingredients ready. Soak poha in water 5 minute or until soft. I used thick poha variety and it was soft enough to mash with 5 minutes of soaking. Thin variety poha might take little longer time. Grind the soaked poha and grated coconut with little water to a smooth paste.
Mash the bananas well with hand or fork. Now in a vessel, add rava, poha coconut paste, jaggery syrup, ghee, cashews, raisins with pinch of salt. Mix everything well. Add water and let it sit for 15-30 minutes.
After 15-30 minutes, poha and rava absorbed most of the water content. Hence adjust with water to make it idli batter consistency that is neither too thick nor thin. Add baking soda if using. Now start making idlis, pour the batter in each idli mould.
Steam it with a cup of water for 10 to 12 minutes in medium flame. Check with a spoon, if it's coming clean, the Idlis are ready! Switch off the flame and remove from moulds.