In a large skillet (about 12-14 inches) over medium heat, cook bacon until crisp, about 5-7 minutes. Add the onions and cook until softened, about 10 minutes. Stir in flour, garlic, and rosemary; cook for 1 more minute. Gradually add the broth, using a wooden spoon or whisk to scrape up any browned bits. Whisk or stir until smooth. Add the Worcestershire sauce, brown sugar, and bay leaf. Remove from the heat. The gravy will be very thick, but that’s good (the liquid and condensation from the slow cooker will thin the gravy as the pork chops cook). Transfer to a slow cooker. Add the apples to the slow cooker (if using).