Chop the bacon up into ½” to 1” pieces.
In a pan over medium heat, cook the bacon until it just starts to get crispy (about 10 minutes).
When your bacon is crispy, remove it from the pan and place it on a paper towel to soak up any excess grease while it cools.
Remove all but two tablespoons of the bacon grease from the bottom of a pan, reduce the heat to low, then add the diced onion and jalapeño (if using).
Saute for 20 minutes, or until the onions are fully translucent and starting to caramelize.
Add the garlic and saute for two to three more minutes until fragrant.
Add the bacon back to the pan with the onions and mix until it is all well incorporated.
Add the brown sugar and balsamic vinegar and mix until well-combined.
Increase the heat to medium-low and simmer, uncovered, for 45 minutes to one hour, stirring occasionally.
Serve immediately or store in an airtight container in the fridge for up to two weeks.
