Roast fenugreek seeds (without oil) till a nice aroma comes out. Make a powder and keep aside (this remains good for a long time when stored in airtight container).
Cook toor dal with mango pieces, turmeric in pressure cooker (about 3-4 whistles).
When pressure cooker is cooled down, mash dal with the back of the spoon.
Add enough water to bring to required consistency.
Add chilli powder, fenugreek powder, salt, kokum(or tamarind), boil it for few minutes. Take off the heat.
Heat a little oil and add mustard seeds.
When they start popping, add curry leaves.
Pour the seasoning over dal.
Serve hot with rice and ghee.
Notes
Fenugreek(methi) powder has a bitter taste. So start with a smaller amount and adjust to your taste.