Rinse the idli rice and urad dal separately under running water until the water runs clear. Soak them in separate bowls with enough water for at least 4-6 hours. Add fenugreek seeds to the urad dal while soaking.

Drain the water from both rice and urad dal. Grind the urad dal first with a little water to a smooth, fluffy batter. Transfer to a large bowl.

Grind the soaked rice to a slightly coarse batter (not as smooth as urad dal). Mix this with the urad dal batter in the large bowl.

Add salt and mix well. The batter should be thick but of pouring consistency. Cover and let it ferment in a warm place for 8-12 hours or overnight. The batter will rise and become slightly frothy.

Grease the idli molds with a little oil. Pour the fermented batter into each mold, filling them about 3/4th full.

Steam the idlis in a steamer or pressure cooker (without the whistle) for 10-12 minutes. Insert a toothpick to check; it should come out clean when done.

Let the idlis cool for a minute, then remove them from the molds using a spoon. Serve hot with coconut chutney and sambar.