Pour cider gravy over slices of this lovely stuffed pork loin roast and pass any extra. Apple slices that have been sauteed in butter are a delicious accompaniment.
Heat oven to 450°F.
Heat 2 tablespoons butter in large nonstick skillet over medium-high heat. Add apples; cook 7 to 8 minutes, until tender but still firm. Remove apples with slotted spoon to a plate.
In same skillet, heat remaining butter. Add onion and celery; cook 10 to 12 minutes, until softened.
Toss together one-third cooked apples, the onion mixture, bread, nuts, sage and thyme in large bowl. Season with 1/4 teaspoon salt and 1/8 teaspoon pepper. When cool, stir in egg.
Set pork, fat side up, on cutting board (remove string if tied). Make long, deep incision lengthwise into side of loin to open like a book; stop 1/2 to 3/4 inch from other side.
Spread meat out flat. Season inside and outside with 1/4 teaspoon salt, 1/4 teaspoon black pepper. Spread stuffing over meat. Fold meat back over. Tie roll at 1-1/2-inch intervals. Set, fat side down, on rack in roasting pan.
Roast in 450°F oven 20 minutes. Lower heat to 350°F. Roast 50 to 60 minutes or until internal temperature of meat is 160°F. Remove to platter; cover loosely with foil.
Remove any fat from pan juices. Place pan over medium heat. Sprinkle with flour; cook, stirring, 1 minute. Add cider, broth and vinegar. Bring to a boil; cook, stirring occasionally, until reduced to about 1-1/4 cups gravy, about 5 minutes. Strain gravy into serving bowl. Season with remaining 1/4 teaspoon salt and 1/8 teaspoon pepper.
Gently reheat remaining sautéed apple slices.
Remove string from roast. Slice meat. Serve with apples and gravy.