In a large, heavy-bottomed pot, cook bacon over medium-high heat until crisp, about 10 minutes. Remove from heat and remove bacon with a slotted spoon and set aside. Carefully remove all but 2 tablespoons of bacon fat from the pot and discard or save for another use.
Return pot to heat, add onions, and cook over medium heat, stirring occasionally, until softened, about 8 minutes. Return bacon to the pot with chopped peaches, brown sugar, black pepper, mustard, Worcestershire sauce, apple cider vinegar, and bourbon (if using). Bring to a boil, reduce heat, and simmer, stirring occasionally, until jam is thick and glossy, about 30-35 minutes. (If your peaches are very juicy and throw a lot of liquid into the jam, this might take a little longer; continue simmering until thick.) As the jam cooks, use the back of your wooden spoon to break up the peaches. Remove from heat and cool to room temperature.
If a smoother texture is desired, transfer cooled jam to the bowl of a food processor and pulse a few times until you reach your desired consistency. Serve jam at room temperature.
