Coat a large saute pan lightly with olive oil. Add the bacon and bring the pan to a medium heat. When the bacon is crispy and has released a lot of fat, add the onions and season with salt. Cook the onions until they are soft and aromatic, 5 to 6 minutes. Add the apples, prunes, and half the chopped rosemary. Cook the apples, stirring occasionally, until they start to soften, about 5 minutes. Pull the pan off the heat and add the brandy. Return to the fire and flambe, or let the alcohol just burn off. Remove from the heat and let cool.
Lay out a length of plastic wrap about 2-feet in length. Spoon the apple mixture onto the plastic and make a log down the center that is about the same length as the pork loin. Roll the plastic tightly around the apple mixture and twist at the ends to secure. The log should be about 1- inch in diameter. Place the log in the freezer and let it freeze solid. This can and should be done ahead of time.
To stuff the pork: Insert a long, thin knife into the center of one end of the pork loin; repeat this process at the other end. Wiggle the knife back and forth to create a place big enough to accommodate your frozen stuffing log. After cutting with the knife, you can use the handle of a long wooden spoon to make sure the incision goes all the way through the pork loin.
Preheat the oven to 375 degrees F.
Get the stuffing log from the freezer and remove the plastic wrap. Slide the stuffing log through the pork loin - it might need a little encouragement but it should go the length of the loin. Season the outside of the pork generously with salt and sprinkle it with the remaining chopped rosemary.
Coat a roasting pan with olive oil and bring the pan to a high heat. Add the pork to the pan and sear it on all sides until it is brown.
Remove the pork to a plate and ditch the fat in the roasting pan. Add the pork back to the pan pour in the chicken stock. Place it in the oven for 25 to 35 minutes, depending on how you like your pork. I personally like it pinker and would remove it from the oven when a meat thermometer reaches 130 degrees F. Turn it over halfway through the cooking time. Remove it from the oven, cover it with foil, and let it rest for 15 minutes before carving.