Heat oil in a pan. Add cumin seeds, mustard seeds, when seeds get splutter add urad dal, chana dal.
Saute the dal till golden brown , add curry leaves. Add Semolina and dry roast until aromatic. Make sure it doesn't changes it colour. Make it cool.
In a bowl add semolina mixture, curd , salt to taste and 1 cup of water. Mix well and keep aside for 30 minutes.
After 30 minutes add 1/2 cup of water or as required. Add baking soda and baking powder. Mix well.
Pour the batter in to a grease the molds with some oil and steam it on a medium flame for 7-8 minutes.
Once it gets cool down, remove prepared idli from it.
Serve with Coconut Chutney.