Sambar Powder:
Tadka (spiced Ghee or Oil):
Place the toor dal and 4 cups of water in a medium pot and bring to a boil, skimming off the foam as best as you can. Adjust heat to medium low, partially cover and simmer, stirring occasionally, until the toor dal is completely soft and most of the water has been absorbed, 45 minutes to 1 hour. Add more water as needed if the dal needs to cook longer. Remove from the heat and use the back of a wooden spoon to mash until creamy. Set aside.
While the toor dal cooks, prepare the sambar powder: In a small dry pan, toast the chiles, chana dal and urad dal over medium heat, stirring frequently, until the dals are golden brown, about 2 minutes; transfer to a small bowl. Add the coriander, cumin, fenugreek and peppercorns to the pan. Toast, stirring frequently, until fragrant, about 2 minutes. Add the curry leaves and toast, stirring frequently, until crisp, about 30 seconds more. Transfer to the bowl, adding the turmeric, and set aside to cool. When completely cool, transfer the mixture to a spice grinder and grind to a fine powder. (Makes about 2 tablespoons of sambar powder.)
Prepare the sambar: Peel the squash, remove the seeds and cut into 1-inch cubes. Peel and chop the potato, carrot and onion into 1-inch pieces.
In a large pot, heat the oil over medium. Add the butternut squash, potato, carrot and onion; stir and cook for 2 minutes. Add the moringa (if using), okra (if using), tomato, chile powder, turmeric and 2 teaspoons salt. Stir and cook for 1 minute. Add just enough water to cover the vegetables (about 4 cups) and bring to a boil. Cover, adjust heat to medium low and simmer, stirring occasionally, until the vegetables are fork-tender but not mushy, about 10 minutes.
Stir in 2 tablespoons of sambar powder, the tamarind paste and the mashed toor dal. Bring to a boil, uncovered. Season with more salt, tamarind and chile powder to taste, being mindful you’ll also be adding the tadka. Stir in the cilantro and turn off the heat.
Prepare the tadka: In the same pan you used for the sambar powder, heat the ghee over medium. Add the mustard seeds and cook until they begin to pop, 1 to 2 minutes. Add the chiles and cook, stirring occasionally, until fragrant, about 1 minute. Stand back and carefully add the curry leaves (they will splatter). Stir until the curry leaves crisp up, about 30 seconds. Pour the hot tadka over the sambar (it will sizzle), stir and serve.
Tips
You can also use pumpkin instead of butternut squash.
Moringa, called drumsticks for their resemblance to the musical implements, are the elongated immature seed pods of the moringa tree native to South Asia. You can buy moringa fresh and cut them into 2½-inch-long pieces, or use pre-cut frozen moringa available at Indian markets. The outer shell of the drumstick is hard and not edible. As you eat, split the drumstick in half and scrape out the flesh and seed with your teeth as you would an artichoke leaf.