Rinse urad dal with water until the water runs clear. Then soak it in a bowl with enough water. Add methi seeds to the soaked dal.
Rinse idli rice with water until the water runs clear. Soak it in a separate bowl.
Soak the dal and rice for 4 hours or overnight.
Drain the water from the dal and rice.
Transfer the dal to the high speed blender (or a wet grinder) and grind to a smooth paste. Add cold water or ice cubes (about 1/2 to 1 cup) as needed to grind the dal. Transfer the batter in the instant pot steel insert (or another large bowl if not using instant pot).
Transfer the soaked idli rice to the grinder and grind to the smooth paste. Add cold water as needed to grind to a fine paste (about 1.5 cups). Transfer the batter to the same instant pot steel insert.
Add salt and mix the batter well using your clean hands for a couple of minutes. The batter consistency should neither be thick nor runny, but rather it should be free flowing.
Fermenting in Instant Pot
Place the steel insert in the instant pot and cover with a glass lid (do not use the instant pot lid, as sometimes batter can overflow and lock the lid).
Set the instant pot to Yogurt mode for 12 hours by pressing the Adjust and + buttons.
After the time is complete, the batter would be fermented and ready to use. If the batter has not risen well, ferment it for couple of more hours. The batter should be frothy and airy on the top.
Enjoy idli or dosa made with the batter.
Fermenting batter without instant pot
If fermenting without the instant pot, transfer the batter to a large bowl and prepare it as mentioned adding salt and mixing with clean hands. Then place it in the oven with the lights on (or on the counter in warm climate).
Steaming Idli in Instant Pot
To make idli, grease the idli molds with ghee or oil. Then add small amount of batter in each mold. If making in the instant pot, add 1.5 cups of water to the instant pot and let it boil in sauté mode. Place the idli stand in the instant pot and cook it in steam mode in venting position. The thing to note is that the timer on the instant pot does not work in the venting position, so you have to use a separate timer. In 12 minutes, the idli will be ready. Let it stand for 5 minutes, then take the idli out of the mold. Enjoy with sambar and coconut chutney.
If you are new to making Idli Dosa Batter, then I highly recommend reading the whole post as I share lots of tips and tricks to get the perfect batter.