Ingredients
1/2 tsp black peppercorns
1  tsp cumin seeds
1 tsp coriander seeds
1 tsp dry curry leaves
4-5 red chillies
Cooking oil for roasting( about 1-2 tsp)
3/4 cup toor dal
2 medium tomatoes , chopped finely
2 tsp jaggery water( or 1 tsp sugar)
3 garlic clovettes crushed coarsely
1 tsp mustard seeds
1 tsp cumin seeds
1 sprig fresh curry leaves
A pinch of hing(asoefetida)
Salt to taste
2 tsp ghee for seasoning

Method
Roast the first 5 ingredients in a little oil and 
grind in a coffee grinder to a smooth powder.
Set aside.(This is the rasam powder)
Boil the dal in a pressure cooker till soft and set aside.
Add the chopped tomatoes, rasam powder, 
jaggery water and salt to taste to the boiled dal.
Heat the ghee in a saucepan and prepare the seasoning
with the garlic, cumin, mustard, hing and curry leaves.
When the mustard starts crackling, add the tomatoes and
dal.
Add enough water to get the required rasam consistency.
Boil till the tomatoes are well cooked on a low flame.
Take it off the fire.
Eat when hot with rice.