Wash and soak horse gram, urad dal, and idli rice separately for 5-6 hours.

Add fenugreek seeds to the soaked rice about an hour before grinding.

Drain horse gram and grind into a thick, smooth batter.

Transfer the horse gram batter to a large vessel.

Drain rice and grind into a smooth paste.

Add the rice batter to the horse gram batter.

Grind urad dal into a smooth and fluffy batter.

Add the urad dal batter to the horse gram and rice batter.

Add salt and mix well using hands.

Keep the batter at room temperature for 6-8 hours to ferment.

After fermentation, add water to adjust the consistency to that of idli batter.

Pour batter into greased idli plates with a ladle.

Place the idli plates inside the idli cooker.

Steam for about 10 minutes.

Check if the idli is cooked by inserting a toothpick or fork; it should come out clean.

If not cooked, steam for a few more minutes.

Remove idli from the plate and serve.