Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Peel and quarter apples and remove the core. Dice apples roughly. Caramelise sugar, deglaze with apple juice, add apples, bring to the boil and simmer for about 25 minutes.
Peel onion and cut into rings. Bring milk and butter to the boil for the puree. Drain potatoes, add milk mixture and mash with a potato masher. Cut blood sausage into 8 slices and remove skin.
Heat the oil in a coated pan and fry the sausage for about 1/2 minute on each side. Take out, keep warm and fry onion rings in the frying fat for about 3 minutes. Arrange mashed potatoes, applesauce, sausage and onion rings on plates.
Garnish with marjoram.