First step in making Arachuvitta Sambhar is to prepare the tamarind water base. Preferably use new tamarind. You can also use tamarind concentrate which is what I use these days.
If using fresh tamarind, soak a lemon size ball in warm water for 20 minutes. With your fingers, squeeze out the juice and strain the water. Transfer the clear tamarind water to a vessel. Always use a stainless steel vessel to prepare sambhar. If using tamarind concentrate, then directly add the concentrate and warm water to vessel and give it a good mix till it dissolves. Then add your choice of veggies. I added chopped bell peppers and tomatoes. Also add turmeric powder, sambhar powder, salt, slit green chilly and jaggery. Bring this to a boil on low flame. Meanwhile or even before you do any of the above, boil tur dal in turmeric powder + water. Once its done, add water to it an mash the tur dal well. It should not be runny but like a thick batter consistency. Keep it aside for now. Next step is to prepare the ground masala. Dry roast freshly grated coconut in a pan. You can also use unsweetened coconut flakes or frozen coconut for the recipe. Roast till it turns light golden brown. Then add oil to the pan and roast roughly chopped onions, dried red chillies, chana dal, coriander seeds, urad dal and cumin seeds.
Roast till they release an aroma and turn golden. Be careful to not burn them. Take it off the flame and let it cool down. Then grind them to a smooth paste. Once the tamarind mixture comes to a boil, add this ground paste, mix and continue to cook it for 7-8 more minutes. The mixture will begin to froth and thicken. That is your cue to add the mashed tur dal to the vessel. Give it a good stir and take the vessel off the flame after 2 minutes. Garnish with chopped cilantro. Lastly give a tadka. In a tadka pan, add ghee and once its hot, add mustard seeds and fenugreek/methi seeds. Once they crackle, add asafoetida and pour the tadka over the sambhar. Serve this hot along with steamed rice and papad. You can also serve this as a side for dosa/idli/wada.