Heat up oil. Crackle mustard, add fenugreek seeds and asafoetida powder. Add mango WITHOUT THE SALT WATER. Combine everything well.

Cook uncovered for a few minutes till the mangoes almost get cooked. The spatula should cut the cubes easily, and the cubes will look a bit mushy. Add jaggery at this point and combine everything well.

Cook till jaggery melts, and the soup gets thicker. To test its thickness, take a drop in a dish. If it shouldn't roll down much (see the drop in the middle of the dish in the attached video), it's ready.

Turn off the stove at this point. The soup is going to get even thicker as it cools down. LET IT COOL UNCOVERED. Add chilli powder when it cools down by at least 50-60%. It's ready to fill in a jar when it cools down thoroughly.