Soak a Lemon Size Tamarind ball with 1 cup (250ml) hot water. Let it rest for 15 minutes.
In the meanwhile, heat a pan, add 1/2 tsp oil and roast Chana Dal, Urad dal and methi seeds until the dals have turned golden brown.
Keep this aside for cooling. In the same pan, dry roast coriander seeds and peppercorns until you get a lovely aroma.
Now, in the same pan, roast the whole red chillies with few drops of oil and set aside for cooling.
Until the above masala mixture cools, let us extract the tamarind pulp / juice. Sqeeze out the pulp in a vessel, add some more water (1 cup) to squeeze out the balance pulp from the tamarind.
Cook this tamarind pulp with 1/2 tsp Turmeric powder, a pinch of asafoetida powder and salt to taste.
In the meanwhile, grind the kuzhambu masala powder that was set aside for cooling.
The tamarind pulp would take about 10 to 15 minutes to reduce on low flame.After the pulp has cooked and reduced with no raw smell, add the ground coarse powder to the simmering tamarind mixture.
Mix well. Add some jaggery to reduce both heat and tanginess from the tamarind. Allow it to simmer and add some water to adjust consistency.
Check salt again, and add more if required. Switch off the flame and prepare for tempering.
Heat a tempering pan, add 2 tsp sesame oil, mustard seeds and curry leaves. Pour the tempering over the Kuzhambu and serve piping hot.