firstly in a pressure cook 2 tomato, ½ cup toor dal, 2 green chilli, ½ tsp turmeric and 1½ cup water and for 5 whistles.
in a kadai, boil ½ onion in ½ cup water for 5 minutes.
pour in cooked dal, ¼ cup tamarind extract and 1 tsp salt. mix well.
boil for 8 minutes or till tamarind extract gets cooked completely.
further add 2 tbsp sambar powder and mix continuously without forming lumps.
boil for 5 minutes or till sambar gets cooked well.
meanwhile prepare tempering by heating 2 tsp oil.
add in 1 tsp mustard, pinch of hing, 1 dried red chilli and few curry leaves.
allow the tempering to splutter.
pour the tempering over sambar and mix well.
finally, serve tomato sambar or thakkali sambar with rice, dosa or idli.