Soak rice and dhals together in water for 3 to 4 hours. Wash well, drain the water completely. Put it in a mixie or in wet grinder. Add red chillies and salt. Grind it to a coarse paste.
In a kadai put the oil. When it is hot add mustard. When it pops up add bengal gram dhal, urad dhal and frew till it become light brown. Add cashew nuts (break it into small bits), asafoetida powder and fry for a second. Crush pepper and jeera coarsely and add to the seasoning. Then add chopped onion and curry leaves. Fry till onions turn glossy. Add this seasoning to the batter. Mix well. Batter should be thick.
Heat a tawa and grease it. Pour a laddle of batter and slightly spread it. Pour a teaspoon of oil around it. Cook for few minutes and flip it over. Cook till it become crisp and remove.
You can eat this as it is or serve with butter and jaggery. Or with aviyal.