Heat oven to 350°F. Line cookie sheet with foil. Place wire rack on foil.
Arrange bacon in single layer on rack. Bake 20 minutes. Meanwhile, in small bowl, stir together brown sugar and balsamic vinegar.
Turn bacon over; spoon brown sugar and balsamic mixture over bacon slices. Bake 10 to 15 minutes longer or until golden brown. Remove from rack. Cool completely, about 15 minutes.