Soak the Urad Dal: Soak urad dal in plenty of water for 4–6 hours (or overnight). Soaking helps with grinding and fermentation.
Grind the Urad Dal: Drain and grind the dal until smooth and fluffy. Use just enough water to keep the batter thick but pourable.
Prep the Idli Rava: You can soak the rava in water for 15–20 minutes, then squeeze out the excess water or mix it directly without soaking. Both methods work well.
Mix the Batter: Combine the dal batter and rava in a large bowl. Mix well to distribute the rava evenly.
Add Salt: Stir in salt and mix gently.
Ferment the Batter: Cover and let the batter ferment for 8 hours or overnight in a warm place. The batter should rise and feel airy.
Prepare to Steam: Lightly grease the idli molds. Stir the fermented batter gently (don't overmix), then pour it into each mold.
Steam the Idlis: Steam for 10–12 minutes over medium heat. Check for doneness with a toothpick; it should come out clean.
Serve Hot: Let the idlis cool slightly before removing them from the molds. Serve warm with chutney and sambar.