1. In a small cup add tamarind to warm water and let it soak for 10 mins and once it becomes soft, pulp it and extract the tamarind juice out of it. Add more water if required to extract most tamarind juice out of it.
2. In a kadai/wok, add sesame oil and heat it to medium heat. Once hot add in mustard and crackle it. Next add fenugreek seeds, cumin seeds and sauté for a few seconds, add the vengaya vathal and the manathakkali vathal. And salute for 1 or 2 minutes until this the vathals are fried nicely.
3. Next add in the chopped onions and garlic and sauté with some salt until onions are slightly browned.
4. Next add in the tamarind extract and the water cover and boil until the raw flavors of the tamarind is cooked through. This would take about 10 minutes on medium flame.
5. When the tamarind extract is bubbling boiled and all the rawness of cooked off add in the sambar powder. If you prefer more spice add a little bit more of redchilli powder. Add water and cook in covered with a lid in medium flame until the masalas are cooked off.
6. Finally after boiling it down you’ll start to see that the gravy is thickened and has slightly started to ooze oil on the sides.
7. Add in powdered jaggary or sugar to add some sweetness to balance out the sharp taste of the tamarind and spices.
8. Continue to cook in medium flame for about 10 minutes. Vathal kuzhambu would have to reduce nicely and thick to a creamy consistency.
9. Turn off the flame and serve hot with rice and appalam.