Wash the yellow lentils in a colander. until the water runs clear. Soak them covered in water for atleast 30 mins (upto 1 hour is good) in the same pot you'll cook them in.
Once soaked, add salt and turmeric powder to the lentils and water. Bring the pot of to a boil on a medium flame. If you see any foamy impurities, skim them out. Once the lentils have come to a boil, add the chopped green mango. Lower the flame to a simmer and let it cook until the lentils and mango are tender.
Add the chilli powder, tomatoes and the jaggery. Taste and balance the flavours. You want to taste a lingering tangy sweetness. The residual heat in the dal is enough to soften the tomatoes without making them mushy.
In a small fry pan, heat the ghee (use a neutral oil if you'd like to make this vegan). Add the mustard, cumin seeds and whole red chillies and let them bloom and splutter in the oil on a low flame. Add the heeng (asafoetida) and the curry leaves and quickly pour this tempering/tadka to the dal and mix through nicely and take it off the heat. Let it rest for about 15-20minutes before you serve.
Garnish with fresh coriander leaves and serve hot with some steamed basmati rice and side of greens/vegetables or a simple salad. A dollop of thick greek yogurt works wonders!
