Wash the cured pork, dab dry. Cut a pocket in the middle with a long knife (3-4 cm wide). Push the plums into the pocket with the handle of a wooden spoon. Place the pork loin on the fat pan of the oven.
Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 1 1/2 hours. Peel and quarter the onion and put it on the fat pan. Gradually pour on 1/4 litre of water.
Peel, wash and cut carrots and celery into pieces. Clean cabbage, cut into strips and wash. Cook carrots and celery in 1/2 litre salt water for about 15 minutes. Add cabbage after 5 minutes.
Knead flour and butter and bind the vegetables with it. Season with salt and pepper. Remove the meat. Pour gravy through a sieve, fill up to 1/4 litre with water, bring to the boil. Bind with sauce thickener, bring to the boil again.
Season to taste with salt and pepper. Cut meat into slices and arrange on plates with vegetables and sauce. Parsley potatoes taste good with it.