For the compote, peel, quarter and core apples. Finely dice the apples and boil them up in a pot with apple juice, lemon juice and sugar. Cover and simmer at medium heat for 3-4 minutes. Remove from heat.
Peel and wash the potatoes, cut in half depending on size and cook covered in boiling salted water for about 25 minutes.
In the meantime peel the onions and cut them into fine rings. Mix onion rings and flour so that the onion rings are thinly coated all around. Heat clarified butter in a pan. Fry the onion rings until golden brown. Drain on kitchen paper. Wash the parsley, shake dry and chop the leaves finely.
Heat milk and butter in a pot. Drain the potatoes, press them into the hot milk with a potato ricer and stir in (alternatively mash them with a potato masher). Season the puree with salt and nutmeg. Keep warm.
Remove the sausage from the skin. Heat the oil in a pan, crumble the sausage into it and fry it over a high heat while turning. Arrange mashed potatoes, apple compote, black pudding and onion rings on plates. Sprinkle with parsley.