Balsamic Caramelized Onions

In a large skillet, heat oil over medium-low heat. Add onions; cover and cook for 13 to 15 minutes or until onions are tender, stirring occasionally. Uncover; cook over medium-high heat for 3 to 5 minutes more or until golden, stirring occasionally. Remove skillet from heat. Carefully add wine or broth and balsamic vinegar. Return skillet to heat. Cook over medium heat about 2 minutes or until the liquid has evaporated, stirring occasionally. Stir in salt and pepper.