Wash and peel the skin from mango. Slice it into medium size pieces. (For four people a cup of mango pieces will do). Put it in a pressure cooker. Add turmeric powder, green chilli (slit into two) and two cups of water. Close with lid and pressure cook for two to three whistles. Once the steam is subsided, remove the lid and mash the mango pieces well. Pass through a sieve and take out the clear puree. Add one or two more cups of water and make it a thin liquid. Keep it aside.
In a small kadai, put the pepper, cumin, coriander seeds, red chillies and dry fry for few seconds. Remove and cook it. Then grind it to a coarse powder.
Add this powder to the mango water. Add curry leaves and salt. Mix well and bring to boil. When it starts boiling, remove from stove.
Season it with mustard and asafoetida powder. Garnish with coriander leaves.