Soak 1 cup of urad dal and 3 cups of rice separately in water for 4-5 hours.
Drain the water and grind the urad dal into a smooth paste using a mixer grinder. Transfer it to a large bowl.
Grind the rice into a slightly coarse paste and mix it with the urad dal paste.
Add 1 teaspoon of salt to the batter and mix well. Cover the bowl and let it ferment for 8-10 hours or overnight in a warm place.
After fermentation, the batter should have increased in volume. Mix it gently.
Heat a non-stick tawa or dosa pan on medium flame. Sprinkle some water to check if the tawa is hot enough. If the water sizzles, the tawa is ready.
Pour a ladleful of batter onto the center of the tawa and spread it in a circular motion to form a thin, round dosa.
Drizzle a few drops of oil or ghee around the edges of the dosa and cook until the bottom turns golden brown and crispy.
Use a spatula to gently lift the dosa from the tawa and fold it in half. Serve hot with coconut chutney, sambar, or any other accompaniment of your choice.