In a large bowl, whisk together the egg, apple, mustard, maple, liquid smoke, salt, paprika and pepper. Add the ground pork and mix with your hands. Add the Panko bread crumbs and keep kneading until well mixed.
Using a cookie scoop (about 2 Tablespoon capacity) scoop and roll the meat mixture into 20 meatballs.
Heat a large, non-stick skillet over medium-high heat and brown the meatballs, flipping once, about 3 minutes per side.
Immediately transfer the meatballs to a slow cooker set on low. Add 1/2 bottle of the hard cider to the slow cooker insert with the meatballs and cook for at least 2 hours (or until internal temperature of meatballs is 160 degrees).
Meanwhile, to make the gravy, melt butter in a large sauce pan over medium high heat. Add the flour, whisk and cook for about one minute. Whisk in the other half bottle of hard cider and cook for about 1 minute. Whisk in the chicken broth. Bring mixture to a boil and turn down heat to simmer the gravy for about 5 minutes.
Add the salt, sugar, and apple butter and cook for about 5 minutes more. Off heat whisk in sour cream. Taste to adjust seasonings.
Gravy and meatballs can be made a day ahead... store in an air-tight container in the refrigerator.
Serve the hot meatballs and gravy over cooked egg noodles.