Dry roast the coriander seeds, dry red chillies and black pepper corns in a heavy bottom skilled till lightly toasted. Cool the spices down and grind a fine powder.
Making Tomato Rasam
Puree the tomatoes and set them aside. You may also chop them fine. I pureed the tomatoes for a finer texture.
Take a sauce pan. Add pureed tomatoes, tamarind pulp, water, salt and turmeric to the pan. Bring it to a rolling boil.
Once it comes to a boil, add toor dal, spice mix and jaggery. Stir with a spoon and switch off the gas. Please do not boil further once the dal is added. This is very important to remember.
Making Tadka for Rasam
Take a tadka pan (small frying pan). Heat oil in it and add hing and mustard seeds to it. Once the mustard seeds start crackling, switch off the gas and add curry leaves to it. Tadka is ready.
Serving the Rasam
Add the tadka to the piping hot Rasam and serve it in 4 cuos equally. Serve some rice papad/papdoms along the side and sip on the hot and fiery Rasam.
Notes
If you do not have the cooked toor dal, then you may add 1 tbsp of dry toor dal while roastig the spices and roast and grind it along.