Soak rice and urad dal separately in water for 6–8 hours.
Grind them into a smooth batter by adding water as needed.
Mix both batters together, add salt, and allow to ferment overnight.
Heat a non-stick tawa or dosa pan on medium heat.
Pour a ladle of batter and spread it thin in a circular motion.
Drizzle a little oil around the edges.
Cook until the dosa turns golden and crispy.
Fold and remove from the pan.
Serve hot with chutney and sambar.