Cut all onion in rings. Don't make them too thick but also not too thin.
Heat the oil in a big pan and add the onions and the sugar and softly caramelize. Don't let it burn.
Put the vinegar, cinnamon, cloves and the balsamico into the mix and leave to simmer for at least ten minutes on low heat. Taste to see if it is soft enough and thickened to your liking. If not, leave to simmer a bit longer. Leave to cool and put into jars.