Soak tamarind in hot water for minimum 20 mins. Extract tamarind juice from it. Adjust total to be 2 & 1/2 cups - 3 cups.
In a kadai/ pan, heat ghee and roast red chilli, pepper, toor dal, coriander seeds until dal turns golden.Cool down and powder it with cumin seeds.
Take tamarind extract, add chopped tomato and coriander leaves to it.
Boil for 2 minutes, add the ground fresh rasam powder.
Add salt, toor dal cooked water. When it again boils and becomes frothy top, switch off the flame.
In a pan again heat 1 tsp oil, splutter mustard. Add torn red chillies, cumin seeds, asafoetida and curry leaves to it.
Add to rasam.