Heat the oil in a large frying pan
Add the onions and mustard seeds and cook for 5-6 minutes
Add the sugar , chilli sauce and 75ml cold water. Cover and cook on a gentle heat for 15 minutes
Add in the wine and balsamic . Bring to the boil then allow to simmer for 15-20 minutes until syrupy
Serve or put into sterilised jars and store