I highly recommend buying balsamic glaze, it is just so delicious and amazing on salads, crostini, etc! Get the fig one, it's EXTRA delicious! But if you don't have it, you can either (1) make your own by simmering ½ cup balsamic vinegar with a tablespoon or two of sugar until it makes a syrupy liquid, or (2) use a splash of balsamic vinegar and a tablespoon of honey - adjust both ingredients to taste after you've combined them with the sautéed onion and dried cranberries. Just be careful, the mixture is hot!