Step 1Wash the dal thoroughly until the water runs clear. In one saucepan combine the dal, 1 1/2 cups water, the turmeric and 1 teaspoon of oil and bring to a boil. Lower the heat and simmer, covered, until the dal is soft, about 30 minutes. Mash with a wire whisk until softened.
Step 2In another saucepan, dissolve the tamarind paste in the remaining 3/4 cup water over low heat for several minutes. Add the shallots and simmer until the shallots are tender, about 15 minutes. Mix into the cooked dal. Add the sambar powder and salt and simmer over low heat just until heated through.
Step 3Heat the remaining 1 tablespoon of oil in a small, shallow saucepan over high heat until it almost smokes. Add the mustard seeds. When these start spluttering, add the curry leaves and immediately empty the mixture into the simmering sambar. Turn off the heat and garnish with the cilantro. Serve hot.