Rinse and soak the Parboiled Idli Rice and the Urad Dal separately in plenty of Water for 4–6 hours; add the Fenugreek Seeds to the urad dal while soaking to help fermentation.
Drain and grind the soaked Urad Dal with a little of the soaking Water to a smooth, airy batter; grind the soaked Parboiled Idli Rice coarsely with just enough Water to form a soft, slightly grainy batter.
Combine the dal and rice batters in a large bowl, mix well by folding to incorporate air, and season with Salt. Cover and leave to ferment in a warm place for 8–12 hours or until it has risen and looks bubbly.
When the batter is fermented, grease idli molds with a little Sesame Oil and pour batter into the molds about three-quarters full. Steam in an idli steamer or a large pot with a tight lid for 10–12 minutes until a toothpick comes out clean. Remove idlis and keep warm.
Meanwhile, start the sambar: rinse the Toor Dal and pressure-cook or simmer it in Water with a pinch of Ground Turmeric until very soft and mushy; mash lightly and set aside.
Soak a small ball of Tamarind in warm Water for 10–15 minutes, squeeze and strain to extract the tamarind juice; set aside.
Chop the vegetables: cut the Drumstick into 2–3 inch pieces, dice the Eggplant, slice the Carrot, chop the Tomato and slice the Onion. In a pot, bring these vegetables to a simmer in enough Water to cook them until just tender.
Add the tamarind extract and the cooked, mashed Toor Dal to the vegetables, then stir in Sambar Powder, a bit of Jaggery to balance the sourness, and adjust seasoning with additional Salt to taste. Simmer for 6–8 minutes so the flavors meld and the sambar thickens to your preferred consistency.
Prepare the tempering (tadka): heat Gingelly Oil in a small pan until hot, add Mustard Seeds and let them pop, then add Cumin Seeds, broken Dried Red Chilies, a few Curry Leaves and a pinch of Asafoetida. Fry briefly until aromatic but not burnt.
Pour the hot tempering into the simmering sambar, give it a good stir, and finish with chopped Coriander and a small spoon of Ghee for richness.
Serve the steaming idlis with hot sambar on the side (and coconut chutney if you like). Tear a warm idli into the sambar so it soaks up the tangy, spiced gravy and enjoy.
