Heat a bigger pan and add oil. Once it turns hot, temper with mustard seeds, dry red chillies, asafoetida, turmeric powder and curry leaves.
Next, add in the raisins and saute until they all swell up well. Make sure to not burn them.
Now transfer the ground masala paste, add about 1/4 to 1/2 cup water. Mix everything well and let this start simmering.
Squeeze and extract tamarind juice out of the soaked tamarind. Strain and transfer the tamarind juice to the simmering curry.
Also add in jaggery powder. Mix everything well and let this simmer in medium heat for about 10 minutes. Keep stirring so that it does not get stuck to the bottom of the pan.
When you see the oil separating, add in salt as per your taste. Mix and simmer again. You will see gojju (curry) getting thick and turning brown in colour. Add some water if it is too thick.
Finally, it will turn glossy, non-sticky and start leaving the pan. At this point, it is done.
This raisin curry is supposed to be semi-dry, but if you like to have a gravy like consistency, you can thin it down by adding water and then switch off the heat.
Serve immediately with steamed rice, dosa etc or refrigerate it in an air-tight container.