Wash the meat and put it on the fat pan of the oven. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for 1 hour. After approx. 15 minutes add stock. In the meantime, peel and wash the potatoes and cut them into large pieces.
Wash and quarter the apples and cut out the core. Cut the apple quarters into slices. Clean, wash and cut leek into rings. Heat oil in a pan. Fry the potatoes for about 15 minutes.
Season with salt and pepper. Add apples and leek 5 minutes before the end of the frying time. Mix mustard and honey. Spread the meat with it several times during the last 10 minutes. Remove the pork loin. Deglaze the meat with apple juice.
Pour into a pot and bring to the boil. Add the sauce thickener while stirring, bring to the boil again. Wash parsley and chop finely. Arrange meat and vegetables on a plate. Pour a little sauce over the meat slices.
Sprinkle everything with parsley. Add the rest of the sauce extra.