Flamboyant Calf's Liver with Caramelized Onions

INGREDIENTS

• 2 tablespoons chopped flat-leaf parsley
• Coarse salt and freshly ground black pepper, to taste
• 2 pounds calf's liver, sliced 1/2-inch thick
• 3 tablespoons chicken broth
• 1/2 pound sliced Black Forest bacon or other lightly salted bacon, cut into 1-inch pieces
• 3 tablespoons sherry vinegar
• 1 tablespoon unsalted butter
• 2 large onions, halved lengthwise and thinly slivered