Bacon Cheddar Burgers with Tomato Onion Jam

For the Tomato Onion Jam

• 1 tablespoon olive oil
• 1 large sweet onion such as Vidalia, Maui, or Walla Walla, very thinly sliced
• 4 small-medium tomatoes
• 1 tablespoon white sugar
• 1 tablespoon brown sugar
• 2 tablespoons fresh lemon juice from about ½ lemon
• 2 tablespoons apple cider vinegar
• 2 teaspoons kosher salt
• 1 teaspoon dry mustard powder
• pinch of red chili flakes optional

For the Burgers

• 8 slices thick-sliced bacon
• 2 lbs freshly ground chuck OR 80/20 ground beef
• salt and pepper to taste
• 4 thick slices sharp white cheddar
• 4 large soft hamburger buns, with or without seeds
• tomato onion jam