In a large pot, heat the ghee or oil over medium-high. Add the onion, reduce the heat to medium and cook the onion, stirring occasionally, until golden and a little browned around the edges, 10 to 12 minutes. Reduce heat to medium-low, add the garlic, ginger and cilantro stems. Add a little more ghee or oil if your pot seems dry. Season with a pinch of salt and cook, stirring frequently, until fragrant and softened, 3 to 5 minutes.

Stir in the cumin, turmeric and cayenne and cook until fragrant, about 1 minute. Add the tomato paste and cook in the oil to take off its raw edge and deepen its color, stirring frequently and taking care not to burn the paste, about 1 minute.

Add the lentils and stir to combine. Add 8 cups of water and season with salt (about 1½ tablespoons) and black pepper to taste. Partially cover, raise the heat to high and bring to a boil. Cover completely, reduce heat to medium-low and simmer, stirring occasionally to make sure nothing sticks to the bottom of the pot, until the lentils soften, about 15 minutes.

Reduce the heat to low and stir in the cinnamon. Add the tamarind paste or lime juice, 1 tablespoon at a time, tasting as you go to ensure it hits just the right bright and tangy notes to balance the heat. Taste and adjust seasoning as needed, then cover and simmer for 10 minutes more, until all the flavors meld.

Garnish with the reserved cilantro leaves and serve with flatbread or rice, if desired.