Add 1 Tsp of Tamarind paste to 1 Cup of Water. Mix well and set it aside.
Add 3 roughly chopped roma tomatoes to a blender jar and pulse them to lightly puree them.
Now in a heavy bottom pot, add sesame oil on medium heat.
Let it get hot, and add mustards seeds, dried red chilies, green chilies, curry leaves and asafetida.
Once the mustard seeds cracle, add pureed tomatoes, ginger garlic paste, turmeric, kashmiri red chili powder, black pepper and salt. Mix well.
Next add in the tamarind water.
Let the mix boil and let the tomatoes cook.
Now add 2 Tbsp's lentils and add 4 Cups of Hot Water. Adding hot water will ensure to maintain the cooking temperature, so I insist you to add hot water.
Mix and bring ot to a boil. Let the rasam boil for 10 minutes
Add finely chopped cilantro and serve it piping hot.