For Idlis: Soak rice overnight then next day add ½ cup water in it and grind it.Then add salt according to it, then rest the batter for 12-15 mins then add a pinch of baking soda.
Now put the batter in the idli steamer in the medium flame. Keep it for 15 mins and idlis are ready. Serve hot.

For Sambhar: Add 3-4 tablespoons of oil then add mustard seeds, curry leaves, salt, sambhar powder and chilli powder. Cook it for 5 mins and add arhar dall in it. Let it cook for 20 mins. Serve hot with idli.