Heat 1 tbsp of Coconut Oil in a pan and add sambar/pearl onions, hing and few curry leaves. Sauté it on medium flame for about 2-3 minutes till they turn glossy and translucent.
Add vegetables of your choice with cubed tomatoes and just enough water to cook the vegetables. Mix in turmeric powder, jaggery, tamarind puree/paste and salt to taste. Cover and cook for 10-15 minutes till the vegetables are cooked well.
While vegetables are cooking, heat the pan and dry roast all the ingredients listed from Urad Dal to Dry Red Chillies for about a minute. Mix in grated Coconut and roast it along the spices for another minute or so till it turns light golden and aromatic.
Cool and grind these roasted spices and coconut to a smooth paste by adding very little water at time.
Add this ground mixture and mashed toor dal to cooked vegetables and mix well. Adjust the seasoning and add water depending on the required consistency of Sambar. Make sure that the sambar is not too thick or thin. Simmer and bring the whole sambar to gentle boil (takes about 5-7 minutes).
Heat oil in a pan and add mustard seeds, dry red chilli, hing and curry leaves in that order. Transfer the tempering to Sambar when mustard starts to pop and splutter.
Mix in finely chopped coriander leaves and let it sit covered for about 10 mins for all the flavours to blend well. Serve this delicious Udupi Sambar with Idli, Dosas or plain steamed Rice and enjoy.