Bacon Burgers with Balsamic Caramelized Onions

Instructions

1. In a large skillet, cook the bacon over medium heat until lightly browned, but not crisp (8 minutes or so). Transfer the bacon to paper towels to drain. Pour off all but 2 to 3 tablespoons of bacon fat from the skillet. Add the onion, season lightly with salt and pepper, and cover the pan; cook for 2 minutes. Uncover, add a splash of water, scrape up any browned bits from the bottom of the pan. Cover, and continue to cook, stirring often, until the onions are soft and beginning to color- about 10 minutes. Add the vinegar, water, and mustard. Return the bacon to the skillet and bring the mixture to simmer. Continue to simmer, uncovered, until the liquid has thickened and most of it has been absorbed- 2 to 4 minutes. Transfer to a small bowl and let cool. Leave at room temperature for up to 2 hours, or refrigerate for up to 2 days (reheating, as needed).
2. In a large mixing bowl, use a fork to gently combine bacon, ground beef, Worcestershire sauce, 1 teaspoon salt and 1/2 teaspoon pepper. Form into 4 hamburger patties, and press your thumb into the center of each patty to create a deep depression. Preheat your grill. Grill burgers to desired doneness (4 to 5 minutes per side). Toast the buns too, if desired- if you're serving with buns.
3. Serve the burgers topped with warm balsamic- caramelized onions. No additional condiments are needed!  Serve on buns, if desired.