1. Wash the rice and dal in running water 2-3 times.
2. Soak all the ingredients except the salt together in water for at-least 4 hours.
3. Grind the ingredients with little water to a very fine paste. Add upto 2 cups of water while grinding. If you are grinding in a mixie, take time and grind in 2-3 batches. Try not to add a lot of water while grinding.
4. Add in the salt to the batter and mix well to combine.
5. Cover the bowl and allow it to ferment for at-least 12 hours in a warm place.
6. The batter would have almost doubled in volume after the 12 hour fermentation.
7. Mix the batter well and the dosa batter is ready. Store the batter in the refrigerator for up to 3 days and use as required.

For making dosa

1. If the dosa batter is very thick, thin it out by adding very little water.
2. Heat the dosa griddle until medium hot.
3. Add 1/3 cup batter and swirl to completely cover dosa griddle. Sprinkle 1/4 teaspoon of oil or ghee to the dosa. Cook until underside of the dosa is golden brown, about a minute.
4. Loosen the edges of the dosa with a steel spatula. No need to flip the dosa. Remove dosa from the griddle and repeat with remaining batter.
5. Serve hot.