Plain rasam and plain tomatoe rasm are dealt with here. This is a routine preparation in our house. It is generally served with mulakootal or avial.   

thakkali {thakkali} (tamatar) [tomatoes] ~ 2 or 3 cut into pieces.  

tovara-parippu { tuvara-parippu } (arhar- dal)  [tuvar dal] ~ 100 gms roughly half a normal(!) tumbler

Puli { Puli} (imli )  [ Tamarind ]  ~ One  gooseberry sized ball ( to be dissolved in water )

Manjal Podi {Manja Podi}  (Haldi) [Turmeric powder] ~ !/2 teaspoon 

Rasam Powder ~ 2 teaspoons

Perumkaayam { Perungaayam}   (hing)  [ Asofetida ] ~ 1/2 teaspoon powder or a small pinch dissolved in water

uppu  { uppu } ( namak) [ salt ] ~ to taste roughly 1to 2 teaspoon(s)

Kaduku  {Kadugu} (sarsoon) [mustard-seeds] ~ two teaspoons

kariveppela { kariveppalai }   (kardi patha) [ curry leaves ] ~ a few leaves (five to ten )         

kothamalli ila {kothamalli ilai} (dhaniya) [fresh coriander leaves ] ~ a few sprigs !!

Preparation

 Mix the Tamarind with about a glass of water and filter it  residue free and keep the tamarind water  

Take A suitably large vessel and a medium Aappai tavi(spoon )

Pour the tamarind-water into the vessel and boil for about ten minutes with sufficient water . The smell of tamarind must go. Then add the cut tomatoes turmeric powder, rasam powder, about 1/2 a teaspoon of salt, add water and stir.  

Now add the dal cooked well earlier in a pressure cooker (with the rice) !

Add another tea-spoon of salt. Add essential water(about three four glasses) to obtain the right consistency !  

Stir and boil for another five minutes. Just before taking the curry off the  flame add the asofetida and stir

Now in an iluppu chatti (frying pan) heat two tablespoon ghee(butter). as it is steaming add the mustard seeds and neem leaves. Let it crackle let it not burn. Put it on the rasam and Don’t stir .   

Add a few stalks and leaves of Kothmeer leaves.

Rasam is ready ! { Check salt add more if necessary } ~ A little jaggery or 1/4 spoon of sugar may be added and stirred before removing from the flame