Peel and slice your onions
Heat a pan over medium to high heat and add in the olive oil. Then pour in the sliced onions and sauté for 2 -3 minutes, stirring until they start to become translucent.
Add in the balsamic vinegar and turn the heat down to medium low. Continue stirring occasionally for another 5 minutes or until the onions are transparent and a little browned on the edges.