In a wide pan or kadai heat Oil (1 tablespoon), add the Mustard Seeds (1/2 teaspoon), Asafoetida (1 pinch), Black Lentils (1/2 teaspoon) and Chana Dal (1/2 teaspoon), wait for them to splutter and change in color.
Now add the Cashew Nuts (to taste) and once they change color, add Curry Leaf (to taste), Fresh Ginger (1 teaspoon), and Green Chili Pepper (2). Saute till they become crisp.
Next add Semolina (1 cup) and roast for 2-3 minutes under medium-low flame. Rava getting warm and aromatic is enough. You need not roast it much, switch off the flame.
Rava idli mixture is ready. Transfer it to a bowl and allow it to cool.
Once it cools, add Dahi (3/4 cup) and Salt (to taste) to the rava, and Fresh Cilantro (1/2 cup) and mix well.
Now check the consistency of the batter. It should be flowy but little thick consistency. So gradually add 1/4 to 1/2 cup of Water (to taste). Let it sit for 15-20 mins. The batter might become little thick again, so again add little water if required. Meanwhile, grease the idli plates.
Heat Water (to taste) in a steamer / cooker. When the water in the steamer starts boiling, add Fruit Salt (1 teaspoon) to the batter and mix gently, you will see bubbles coming out. Immediately pour in the idly mould and place in the steamer to cook.
Steam cook for about 12- 15 mins. Insert a knife/ toothpick in the center of the idly to check if its done, if it comes clean its done. Switch off the flame and allow it to cool a bit .
Remove the idli's from the mould using a spoon. Serve them hot with Coconut Chutney or Sambar.