How to Make It
In a medium saucepan, cover the dhal with 2 1/4 cups of the cold water and stir in the turmeric. Bring to a boil, then cover and simmer over low heat until the dhal is tender, about 30 minutes. Using a potato masher, puree the dhal, then transfer to a bowl.
Meanwhile, in a heatproof bowl, soak the tamarind pulp in the hot water until it is thoroughly dissolved, about 10 minutes. Strain the tamarind liquid through a coarse sieve and set aside. Discard the tamarind solids.
In a medium saucepan, heat the vegetable oil. Add the mustard seeds, cumin, peppercorns and fenugreek and cook over moderate heat until the mustard seeds start to pop. Stir in the curry leaves, dried chiles and asafetida. Add the dhal to the pan along with the tomato, onion, salt, tamarind liquid and the remaining 6 cups of cold water. Bring to a boil over high heat. Cover the saucepan and simmer the mixture over low heat for 30 minutes. Stir, then allow the solids to settle. Using a ladle, serve the hot broth in large bowls or mugs.