Marinate prunes in beer 6-8 hours or overnight.Make a 3 inch incision along the length of the pork loin and lay flat. Season the tenderloin with salt and pepper. Remove the prunes from the beer, but do not discard the beer as it will be used to create the sauce. Rough chop the marinated prunes and combine with the diced apples and parsley and spread in the center of the open tenderloin. Fold over and secure with silicone cooking bands or twine. Season the outside of the tenderloin with salt and pepper.
Heat olive oil in a Dutch oven on the stove top and place the tenderloin in the pot, searing both sides. Cover and cook on the stove top for 15-20 minutes on medium heat. Add the beer that was used to marinate the prunes, cream and tamari sauce in the pot and continue to cook for 5-10 minutes more. Test with a meat thermometer, making sure the tenderloin is registering 160 degrees.
Remove tenderloin from the Dutch oven and allow to rest for 10 minutes before carving. Serve with sauce from the pot and garnish with additional chopped parsley.
Note: Tamari Sauce is a type of soy sauce that is lower in sodium. It can be found at grocers in the soy sauce section.