Soak tamarind in 2 cups of hot water for 15 minutes. Squeeze the pulp and extract the juice.If using tamarind paste, dilute in 2 cups warm water. Heat a saucepan or heavy bottom pan in low to medium heat and add the gingelly oil.
Once the oil is hot. add mustard seeds and let it crackle. Then add chana dal and urad dal.
Once dals starts to turn golden, add red chillies, asafoetida, fenugreek seeds and half of the curry leaves. Fry for 15 seconds.
Then add the vathal and fry till it is crisp. Turn off the heat.
Add turmeric powder, red chilli powder and sambhar powder. Fry the spices for 30 seconds.
Add the tamarind extract, required salt and combine well.
Turn on the heat. Bring to boil. Once it starts to boil, simmer over low to medium heat for 8 to 10 minutes.
Mix rice flour in 1/2 cup water without lumps. Add rice flour water, jaggery and simmer for another 3-4 minutes in low heat.
Finally add 1 teaspoon gingelly oil and remaining curry leaves.