Dilute the tamarind with water and drain to remove all pulp residue in a bowl. Add turmeric, salt and let it sit aside, while you begin the cooking process.
Rasam Spice Mixture In a mortar, add the coriander seeds and pound it till it's broken up properly. Then add pepper and crush it coarsely.
To this, add curry leaf and garlic with its skin on and pound the mixture together with the spices.
It does not have to be fine, just coarsely pounded. Leave it covered in the mortar.
Soup base Heat oil and saute the spices for tempering. When the mustard seeds stop spluttering and the onions turn translucent, add the tamarind stock and bring it to boil.
To the boiling stock, add the resam spice and simmer over low heat for about 5 mins, till the garlic is cooked. At this stage, you may add tomatoes, if you like it slightly sour.
Add chopped coriander leaves as garnish before serving.
Note: This is a very basic recipe for the beginners. The spices and the sourness can be adjusted as one desires.Resam can be made plain, with dhall, beetroot, pineapple, coconut water or milk. And the list goes on.