Wash the rice 2 to 3 times with water and soak in water for a minimum of 4 hours (overnight soaking is fine too)
Wash the dal 2-3 times and soak it separately for the same time period as the rice
Blend the dal first into a smooth paste and then transfer it to a big bowl
Then blend the rice till it's finely ground as well (though it need not be as soft as the ground dal) and transfer it to the same bowl.
Add salt and mix well for about 3-5 minutes by hand
Cover and set aside undisturbed for 6-8 hours
After 8 hours, open the lid. You will see the batter is fermented and ready to be cooked
Apply a thin layer of oil to all the idli slots. Using a ladle, put some batter into each slot.
Boil a cup or more of water in the steamer bowl and place the stand in it. Cover the bowl and cook for 8-10 minutes. You can use the pressure cooker too as a steamer, but make sure you do not put the vent weight on the top, as the steam has to escape.
After 10 minutes turn off the stove and wait for a couple of minutes. Take out the idli racks. Using a blunt knife or a spoon remove the idlis to a plate.
Dab a little ghee (optional) on each and serve with chutney & sambar
Enjoy your idlis!