Add onion and garlic to the same pot and cook until soft and translucent (about 10 – 12 minutes), stirring occasionally. Return the bacon to pot along with the brown sugar, brewed coffee, apple cider vinegar, maple syrup and water, stirring to combine. Bring the mixture to a boil, then reduce to low and simmer uncovered for 2 1/2 hours, stirring every once in a while to prevent sticking, until thick and dark brown in color.