Idli with Sambar

Rinse the idli rice and urad dal separately until the water runs mostly clear. Soak the rice in one bowl and the urad dal with fenugreek seeds in another, covered with plenty of water, for 5-6 hours.
Drain both and grind separately with a little fresh water into smooth batters. Combine in a large bowl with 1.5 tsp salt and mix well; the batter should be thick enough to coat the back of a spoon.
Cover loosely and let ferment in a warm place for 8-10 hours, or overnight, until visibly risen and slightly bubbly.
Grease idli molds lightly with oil. Gently spoon the fermented batter into each mold without stirring too vigorously, filling about three-quarters full.
Steam the idlis in a steamer or large pot with a rack over boiling water for 10-12 minutes, covered, until a toothpick inserted comes out clean and the tops spring back when touched.
Remove from the steamer and let cool for 2 minutes before running a wet spoon around the edges to unmold each idli. Set aside covered to keep warm.
For the sambar, combine the toor dal, water, and turmeric in a pot. Bring to a boil, then reduce heat and simmer, partially covered, for 20 minutes until the dal is completely soft and mushy. Whisk with a spoon to break it down further.
Add the carrot, eggplant or okra, onion, and tomato to the dal pot, and simmer for 10-12 minutes until the vegetables are tender.
Stir in the tamarind paste, sambar powder, and 1 tsp salt. Simmer for 8-10 minutes, stirring occasionally, until the flavors meld and the sambar thickens slightly to a soup-like consistency.
In a small pan, heat the oil over medium heat. Add the mustard seeds and let them pop for 20-30 seconds, then add the curry leaves, dried red chilies, and asafoetida, cooking for 15-20 seconds until fragrant.
Pour this sizzling tempering over the finished sambar and stir through immediately.
Taste and adjust salt or tamarind, then serve the hot sambar alongside the steamed idlis with coconut chutney.