While the onions are cooking, chop up the crispy bacon into bacon bits and then add them to the pot with the onions. Add in the Worcestershire sauce, apple cider vinegar and the brown sugar and stir together. Let the onions cook, uncovered, stirring occasionally for about 30 to 45 minutes. Reduce the heat to low and continue cooking until the onions are a rich, brown color, for about 10 minutes, stirring frequently. Remove from the heat and set aside.