For the spice paste, clean 1 chilli pepper. Lightly roast the grated coconut, coriander and chilli in a pan while stirring constantly. Grind finely in the universal chopper. Gradually add 100 ml water.
Onions peel and cut into cubes. Boil 3/4 litre of water. Bring the lentils, onions, turmeric and chilli powder to the boil, simmer for about 15 minutes until the lentils are almost soft. Peel and wash potatoes and carrots.
Dice the potatoes and cut the carrots into 2.5 cm long pieces. Add carrots, potatoes and beans to the lentils, bring to the boil and simmer for another 10 minutes. Season with salt and tamarind concentrate.
Add the spice paste and mix. Heat the oil in a small pan. Roast the mustard seeds while stirring for approx. 3 minutes. Clean the rest of the chilli peppers. Coarsely chop curry leaves and chillies and add to the mustard seeds.
Arrange kootu sambar in bowls. Sprinkle with roasted mustard seeds.