Heat 1 tablespoon of oil in a frying pan (skillet) over low heat.
Add the mustard powder, fenugreek and asafoetida.
Stir-fry for about 30 seconds.
Heat 375ml / 13fl oz (1½ cups) oil in a large, heavy-based pan over low heat.
Add the mangoes and fry for 20 minutes, or until they soften.
Remove from the heat and allow to cool.
Transfer to a blender or a food processor.
Add the fried spices, chili powder, turmeric, and remaining oil and season with salt, then process until ground.
Transfer to a bowl.
Heat the oil for the tempering in a frying pan over medium heat.
Add all the ingredients and stir-fry for about 1-2 minutes, or until brown.
Remove from the heat and allow to cool.
Then mix with the mango and spice mixture.
When cool, this chutney can be stored in airtight ceramic jars for several months.