Add the chopped bacon to a large skillet and place it over medium heat. Cook the bacon until it's crispy, stirring occasionally, about 10 minutes. Use a slotted spoon to transfer the bacon to a paper towel-lined plate to drain. Reserve 2 tablespoons of bacon grease in the skillet.
Add the onion to the hot bacon grease in the skillet. Stir to coat in the grease. Reduce the heat to low and cook, stirring occasionally, for 25-35 minutes until the onions are caramelized.
Add the brown sugar, apple cider vinegar, bourbon, balsamic vinegar, and maple syrup to the skillet. Stir until combined. Bring to a simmer and cook for 15 minutes over low heat, stirring occasionally.
Add the bacon back to the skillet and stir. Continue to simmer the jam for 10-15 minutes, stirring occasionally, until thickened and bubbly. (Keep in mind the jam will thicken more as it cools.) Remove from the heat and serve warm or let cool to room temperature.
Notes
Store leftovers in the fridge in an airtight container for 2-3 weeks. Freeze for up to 3 months. Thaw in the fridge overnight before using.
Brewed coffee can be substituted for bourbon for a booze-free jam. Use the same 1/4 cup amount.