6 bacon slices, cut crosswise into 1/4 inch wide strips
4 boneless, skinless chicken breasts
1 pound white onion, diced
1 head garlic, cloves separated and peeled
1/4 cup balsamic vinegar
Cook bacon in a deep 12 inch heavy skillet over moderately low heat, stirring, until crisp, about 8 minutes.
Transfer bacon to paper towels to drain and reserve bacon fat in skillet.
Pat chicken dry and season with salt and pepper.
Brown chicken in 2 batches in bacon fat over moderately high heat, turning about 8 minutes.
Transfer chicken as browned with tongs to a plate and pour off all but 2 tablespoons fat from skillet.
Add onions to skillet and cook over moderately low heat, covered, stirring occasionally, until soft and pale golden, about 10 minutes.
Remove lid and cook onions, stirring until deep golden, about 10 minutes more.
Add garlic and 1 cup water to skillet and boil, stirring, 1 minute.
Return chicken to skillet, turning pieces to coat, and gently simmer, until chicken is cooked through and garlic is tender, about 20 minutes.
Transfer chicken to a serving dish.
Add vinegar to sauce and boil, uncovered, mashing garlic with back of spoon, until slightly thickened.
Season sauce with salt and pepper and pour over chicken, then sprinkle with bacon.
NOTE: I like to cut my chicken breasts into strips. Also, mashed potatoes are the ideal accomaniment to this dish.