Wash the dal, take it in a vessel add twice the amount of water, a pinch of turmeric and pressure cook it until soft.
While the dal is cooking, soak tamarind in warm water for 15 minutes. This can be done overnight also. I do it sometimes to ease cooking in the morning. Extract tamarind water. Add extra water to this and bring it to 3.5 - 4 cups of tamarind water.
Take the extracted tamarind water in a heavy bottom sauce pan. Add chopped tomatoes, curry leaves, green chili and hing to this. Let this start to cook.
Take the spicesm given under "To pound' in a mortar-pestle or in a spice grinder and make a coarse powder. You can alternatively use your rasam powder also.
Add the spice powder, salt and turmeric powder to this tamarind-tomato mix and let this come to a boil. Reduce the flame and let it cook for 10-12 minutes.
By this time the rawness of the spice powder would have vanished and you will start smelling the divine aroma of rasam.
By this time, the pressure cooker would have released, remove the cooked dal, mash it well. You might not need the entire dal for the rasam, remove 2-3 tbsp of cooked dal to another bowl. Mash the rest and add it to the boiling rasam, add 1/2 cup water, check consistency, if too thick add another 1/2 cup of water.
Simmer the flame and let this sit for another 5-8 minutes until it froths beautifully. Keep the flame low, or else it will start to boil. To this now add some pounded ginger and fresh coriander leaves. Take it off the heat.
In a tadka pan, heat oil splutter mustard seeds, cumin seeds, red chili, finally add pepper powder to this. Pour the sizzling tadka over the hot rasam. Keep it covered for 10 minutes.
Serve this flavorsome paruppu rasam with rice and ghee for a warm and comforting meal.
The rasam can be left on the kitchen counter covered for 5-6 hours. Any leftovers can be refrigerated for 2 days.