Make a powder of coriander seeds, cumin seeds and black pepper. Keep aside.
Add warm water to tamarind, soak for 15 mins, extract tamarind paste and keep aside.
Powder the Bengal gram and add to about 2 ltrs of water.
Mix the above well and boil.
:- The water turns pale yellow.
Add salt and tamarind paste.
Pound garlic pods to a rough paste and add to the boiling gravy.
Add some more water (a glass or two) and continue boiling.
Add the rasam powder made earlier to the boiling rasam.
Heat oil in a pan.
Splutter mustard seeds and saute curry leaves.
Add this to the boiling rasam.
:- Add tomato pieces (100 gms) at step 5 (optional).
:- Add split green chillies at step 6 (optional).
:- Adding a pinch of asafoetida(Kaayam) at step 10 is also optional.