Peel the onions, then cut them in half and thinly slice.
Heat the oil in a heavy-based pan. Add the onion and cook at low temperature for 10 minutes until soft.
Add 3 Tbsps of sugar to the onion and turn up the heat. Cook for 3-4 minutes, while constantly stirring (make sure it doesn’t burn!).
When the onion is golden brown, pour over the vinegar and add the remaining ingredients. Stir, then simmer for 15-20 minutes.
When it turns into a dark brown, thick, jelly-like jam, turn off the heat and spoon the chutney into cooled, sterilized jars. Seal the jars well.