Wash, drain and cook toor dal in 2 cups of water until soft. Strain and mash cooked dal well. Reserve the strained cooking liquor. Clean, wash and finely chop fresh coriander leaves. Reserve 2 tablespoons chopped coriander leaves for garnish.
Soak tamarind in 1 cup warm water; remove pulp, strain and reserve. Wash and chop tomatoes. Remove stems and break red chillies into 2.
Mix tamarind pulp with chopped coriander leaves, rasam powder, asafoetida powder, salt and 1/2 the quantity of curry leaves and bring to a boil. Reduce heat and simmer for 2-3 minutes.
Add chopped tomatoes and the reserved cooking liquor. Simmer for 4-5 minutes and add mashed dal. Stir well and cook for a minute more. Remove from fire and sprinkle the reserved chopped coriander leaves.
Heat pure ghee in a tempering pan, add mustard seeds and stir-fry till they crackle. Add broken red chillies and remaining curry leaves and stir well. Pour the tempering over the prepared rasam and cover immediately to trap the aroma. Serve hot.
NOTES: You can strain this rasam and serve in small tumblers with a lemon wedge, as an appetizer. Traditionally, all rasams are made in a vessel made from a special aloy. This gives a unique flavour to the preparation.
