1. Sambar Powder: in a blender/food processor, combine 1c dhal (eg, urad, channa, tuar, masoor), 1T cumin seeds, some mustard seed, some pepper corns, and red chilli. The friend who gave me this recipe suggested "20" (thank you, I did not).
2. Veggies, etc.: heat coconut oil and add a generous amount of cumin seeds and some mustard seed. Wait for them to pop. Next, add onion, carrots, potatoes, radish, etc. Sautee. Add green veggies, too. I used a lot of okra, two different green gourds, corn off the cob, tomatoes and green onion stems.
3. Soup: When things are starting to look good, add water, veg. bouillon, your sambar powder, some curry leaves and tamarind paste. Sitr, cover and wait. Before the veggies are cooked all the way, turn off the heat and let cool. Add some fresh lemon juice and coriander = parsley before you serve.
My dad and I ate this over fresh flakes (bajri, jowar, vargu and ragi, all of which are different kinds of millet grown in the South; sorry, I don't know their English names -- I don't even know what vargu and ragi are in Hindi, so I can't find them here!) which I'd soaked in some broth.
Obviously, you can use any veggies you like for the soup.
And, a traditional sambar would have added dhal to the cooking veggies and would have been served with cooked rice (eg, red rice or the huge! white Keralan rice), not flakes.