In a medium-sized soup pot (or high-sided sauce pan) over medium heat, melt the butter then add the yellow onion. Cook the onion until soft and translucent (approximately 5 minutes).
Add the minced garlic and continue to cook for 1 minute.
Add the ketchup, bourbon, chipotle pepper, adobo sauce, cider vinegar, balsamic vinegar, honey, and dark brown sugar. Lower the heat to low and stir to combine.
Allow the sauce to simmer for 30 to 40 minutes over low heat.
Using an immersion blender, process the sauce until smooth.
Add the celery salt and black pepper. Stir to combine.
Remove from the heat and allow the sauce to cool to room temperature.
Use immediately or transfer into an airtight container and chill the sauce in the refrigerator for up to a week (the sauce will gain in spiciness during this time).