Wash pigeon pea/ toor dal couple of times until the water comes clean.
Take the washed toor dal, chopped tomato, green chillies, turmeric powder, salt in pressure cooker along with 1 cup of water. Cook it in medium flame for 4 whistles. Switch off the stove and allow it to cool.
Once the pressure is released completely open the lid. Mash the dal to smooth using the back of the spoon.
In a cooking pot, take tamarind solution, jaggery powder, salt, 1 cup water and mix well. Now simmer this in medium flame till it comes to boil.
Now add cooked dal, 1 cup of water and mix well. Simmer again in medium flame till it comes to boil.
To this add udupi rasam powder and stir well. Cook for 2 minutes.
Now add chopped coriander leaves and cook for another 1-2 mins.Switch off the stove.
For tempering, heat 1 tbsp oil in small pan. To this add mustard seeds, as they crackle add broken dried red chilli, curry leaves and asafoetida. Fry this for one minute. Switch off the stove.
Pour the tempering to rasam and mix well.