I learnt this from mother in law, actually she learnt this from her grandfather who was running a famous vegetarian hotel of that time.
Udad dal ½
Tovar dal ¼ cup
Channa dal ¼ cup
Moong dal ¼ cup
Methi seeds ½ tsp
Soak all the ingredients for 4 to 5 hour then grind into fine paste.
Add salt mix well keep aside for 6 to 7 hour for fermentation.
Next day morning heat dosa tawa and prepare thin and crispy dosas. Serve with spicy coconut chutney. yummy yummy tummy full..:P