Wash the millets well and soak in 4 cups water for at least 4 hours.
Wash the udad dal till water runs clear and soak it with the fenugreek seeds in 2 cups water for at least 4 hours.
Drain and discard all the water from the millets.
Grind the millets to a fine paste.
Drain and reserve some water from the udad dal and fenugreek.
Add the udad dal and fenugreek to the ground millets.
Grind to a smooth and thick paste using some of the reserved water.
Take the batter out into a large enough vessel and let it ferment for at least 4 hours or till the batter rises. It won't rise as much as the regular idli batter.
Making the Idlis
Add water to the steamer/pressure cooker, and let the water start boiling.
Add salt to the batter and mix with a very gentle hand.
Grease the idli mould with a few drops of oil.
Add enough batter to each cavity to just fill it.
Place the Idli stand in the steamer/pressure cooker and steam for 5 to 7 minutes.
Turn off the heat and let it cool for about 5 minutes.