Soak idli rice, dosa rice, urad dal and methi seeds in enough water for 6-8 hours.
Grind it into a smooth batter in a wet grinder or mixer sprinkling water as needed.
Add salt as needed and mix it using hand. Let the batter ferment overnight, it would double up in bulk.
When ready to make dosa, mix the batter well and add some water if needed. The batter should be thinner than idli batter.
To make crispy dosa -
Heat the dosa tawa on medium flame. When it is hot enough, grease it with few drops of oil and rub it in using an onion. When drops of water are sprinkled, it should sizzle.
Pour a ladle of dosa batter at the center of the dosa tawa.
Spread it as thin as possible on the hot tawa. Sprinkle few drops of oil all over the edges and cook the dosa until it is golden brown in the bottom.
Gently remove it from the pan. Fold it in half.
Serve hot with coconut chutney, chutney podi or sambar.