Add the rice and dhals to a bowl. Rinse until the water runs clear, then soak for 30 mins.
Pour 1/2 a cup of boiling water over the tamarind. Break it up and let it sit for 10 mins.
Add the tomatoes, garlic, green chilli, cumin seeds, coriander seeds, and peppercorns to a blender jar. Pulse a few times to get a coarse paste.
Add 1 cup of room temp water to the bowl containing the tamarind. Squeeze with your fingers to get most of the pulp into the water. Retain the tamarind water and discard the pulp.
Heat ghee in a pressure cooker (or a heavy-bottomed pot). Add the mustard seeds and urad dhal. When the seeds starts to splutter, add the dried chillies, curry leaves, and asofoetida. Stir for a few seconds.
Add the blended paste along with the tamarind water. Season with salt. Cook over medium heat for 10 mins.
Drain the rice and dhals and discard the water. Add the rice and dhals to the pressure cooker. Add turmeric powder. Pour in 5 cups of fresh water.
Pressure cook over medium heat for 5 whistles (about 10 mins). Let the pressure release naturally.
Remove the lid, and stir the rice and dhals vigorously to break up some of the rice. Add a little hot water if necessary to get a looser consistency.
Stir in the coriander. Taste and adjust seasoning. Serve hot.