For bacon tomato jam: In a 12-inch cast-iron skillet, cook bacon over medium heat until almost crisp. Remove bacon using a slotted spoon, and let drain on paper towels, reserving 3 tablespoons drippings in pan.
Add onion to skillet; cook until lightly browned, 3 to 4 minutes. Stir in all tomatoes, brown sugar, vinegar, garlic, salt, and pepper; cook, stirring occasionally, until thickened, 30 to 35 minutes. Transfer mixture to a medium bowl, stir in bacon, and let cool completely. Wipe skillet clean.
For burgers: In a large bowl, stir together beef and salt. Divide mixture into 6 portions, and shape each portion into a 5-inch patty.
In same skillet, cook red onion over medium heat until tender. Remove from skillet. Cook patties for 6 to 8 minutes per side or until desired doneness, brushing with ¼ cup bacon tomato jam during last minute of cooking. Add 2 slices cheese to each patty; cook until melted.
On bottom half of buns, layer red onion, patty, bacon tomato jam, and top half of rolls. Serve immediately.
Recipe by Southern Cast Iron at https://southerncastiron.com/double-cheese-burgers-with-bacon-tomato-jam/