Wash the orange, dab dry and cut in half. Remove the offal, neck and fat from the goose. Wash goose thoroughly inside and outside. Season belly with salt and pepper. Fill goose with orange halves.
Plug the neck and belly opening with wooden skewers. Tie up with kitchen string. Tie legs and wings together. Season the goose with salt and pepper on the outside and put it on the fat pan of the oven. Pour on 1/4 litre of water.
Roast in the preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see manufacturer) for 3 1/2-4 hours.
In the meantime, clean and wash the celery for the filling and cut it into small pieces. Peel and finely chop the onion. Wash sage, shake dry, pluck leaves and chop finely. Cut bread into small pieces.
Heat the oil in a large frying pan. Sauté the onions for 2-3 minutes while turning. Add celery and steam for about 2 minutes. Add minced pork and fry for 4-5 minutes until crumbly. Add bread pieces and sage about 1 minute before the end of the cooking time.
Season vigorously with salt and pepper.
Wash apples and grate them dry. Cut off the upper lid and remove the core with the apple corer. Spread the minced filling on the apples.
Mix 150 ml boiling water and about 1 1/2 teaspoon salt until the salt is dissolved. Brush the goose with salted water about 30 minutes before the end of the cooking time and spread apples around it.
Wash the plums, drain, cut in half and remove stones. Cut plums into small pieces. Lift the goose from the fat pan and keep warm. Pour gravy through a sieve into a pot and degrease.
Top up the gravy with stock and port wine. Add plum pieces, bring to the boil and simmer for about 8 minutes. Stir in jelly about 2 minutes before the end of the cooking time. Mix 4 tbsp. water and starch.
Bind the sauce with it, bring to the boil again and season to taste with salt and pepper.
Arrange goose and apples on a plate. Garnish as desired with fresh bay leaves.