In a bowl, soak idli rava, sago and sour curd.
Mix well.
Cover this and keep it aside for 8 hours or overnight.
Next day, in a pan, add oil and add mustard seeds, asafoetida, chana dal, and urad dal.
Once dal turns the golden color switch off.
Add to the idli rava mixture.
Mix well and add water to bring the idli batter consistency.
Add salt and grated coconut mix well.
If you want you can add ½ tsp of baking soda to get soft idlis.
Grease idli mould with few drops of sesame oil.
Pour batter in idli moulds.
Steam for 10 minutes. To check insert a toothpick in the center and if that comes out clean, idli is ready.
Take out from mould after a minute.
Dip a spoon in water to take out the idlis from the mould.
Serve with Kara chutney or sambar.