Soak the tamarind in water for 15 minutes. Extract the tamarind juice and discard the fibrous pulp. Set it aside.
Grind together coconut, coriander stem, one small onion, garlic, one small tomato, and sambar powder using ½ cup of water. Set the masala paste aside.
Take a heavy bottom pan or kadhai and add oil. Once it heats, add the mustard seeds.
Once they crackle, add cumin seeds, curry leaves, and hing.
Add one small onion and saute for 3-4 minutes or until they are translucent.
Add sprouted horse gram and saute for 3-4 minutes.
Add the ground masala, moong dal, salt, tamarind extract, and one small tomato.
Add 5 cups water and mix well. Bring to a rolling boil.
Cover and let it cook on medium heat. This can take 40-45 minutes.
Cook until the horse gram is fully cooked. Alternatively, pressure cook for 4 whistles
Turn off the heat and add cilantro. Serve hot with rice or roti.