Balsamic Marinated Onions

Preheat oven to 375 degrees F. Cut the onions in half, peel off the outer layer of skin and slice thinly. Toss in a medium-size pan with olive oil, balsamic vinegar, salt and pepper. Cover the pan tightly and bake for about 45 minutes, or until the onions are tender. Stir in the capers and season to taste with additional salt and pepper.