Heat oil in a frying pan. Add mustard seeds. When they crackle, add jeera, urad dal, chana dal, curry leaves, hing, and grated carrot (optional). Fry on a low to medium heat for 5 - 8 minutes or until crisp.
Mix idli batter with seasoning. Stir well continuously for 2 minutes.
Grease each idli mould with little oil. Arrange 3 - 4 cashew nut splits (shallow fried or normal) on each idli mould. Pour idli batter over it very gently and steam in steamer / slow cooker / steam in pressure cooker (without weight) for 15 - 18 minutes on a medium heat. Allow it to cool for 10 - 15 minutes and remove carefully. Serve with coconut chutney / sambar / tomato chutney.
Grind all the ingredients to a smooth paste with a little water. Adjust the thickness of the chutney with extra 2- 3 tbsps water if you required.
In a pan, heat 2 tsp oil. Add mustard seeds. When they splutter, add remaining ingredients. Saute well. Pour this over the coconut chutney.