If you have medium sized onions, or if you are rushed to get dinner done, cut the onions in half, but ideally keep them whole
Add the onions to the water and simmer until the onions are soft.
Add a little water, to ensure that the onions are lying in about 1cm of water, add the sugar and balsamic vinegar and simmer, gently turning them occasionally. If the water cooks dry too quickly just add a little more. Once the onions are coated with a sticky, but not toffee like glaze, they are ready.
Serve hot or at room temperature.
In Italy the onions are served as part of an antipasti selection.