Rinse 3 cups of rice and 1 cup of urad dal, then soak them in water for about 2-3 hours.
Drain the water and grind the mixture in a blender, adding enough water to make a paste.
Add 1 to 1 1/2 teaspoons of salt to the paste and set it aside to ferment for 12 hours.
Grease each idli mould on the idli plates with a drop of oil, spreading it evenly.
Fill the greased idli moulds with the fermented batter.
Heat 2 cups of water in a large vessel or pressure cooker, then place the filled idli plates inside and cover with a lid.
Cook on high heat for about 20 minutes.
Carefully remove the idli plates from the vessel and take out the idlis.
Drizzle 2 teaspoons of sesame oil over the idlis while serving.
Serve with side dishes such as sambar, dosai milagai powder, and coconut chutney.