Heat coconut oil in a pan. Chop the onions and fry them in the oil. Add salt, chilli powder and a sprig of curry leaves and fry till onions are slightly brown. I use kashmiri chilli powder because it gives the colour and flavour but not too much heat.
Turn off the heat and cool the mixture. Blend it in a mixer to a paste.
Heat coconut oil in the pan. Splutter mustard seeds and add more curry leaves. Lastly, add the blended paste into the pan and fry for 5 minutes. Add more chilli powder if you like your chutney very spicy.