Although you can purchase balsamic reduction – the thick syrup made from the vinegar of the same name – it is much much cheaper to make it yourself, and nothing more than what its name suggests : a reduction of balsamic vinegar.
It adds sweetness and depth to any dish if you sprinkle it on top before serving : steamed vegetables, pasta, a salad, a nice bruschetta… It will also make them look much fancier.
You could customize it by adding other types of vinegar inside or some fruit cordial, but I like it simple and pure most of the time.