Peel and chop the onion. Heat 2 tablespoons of oil in a saucepan. Fry the onion in it. Add sauerkraut and braise a little. Deglaze with wine and apple juice. Add bay leaf, juniper berries and peppercorns.
Covered sauerkraut and braise over medium heat for about 40 minutes. Peel, wash and halve the potatoes. Boil potatoes covered with salted water and cook for about 25 minutes. Heat up milk. Drain potatoes and mash roughly.
Add milk and fat and mix. Season to taste with salt and nutmeg. Heat the rest of the oil in a pan and fry the sausages until brown all around. Season the sauerkraut with salt again. Arrange mashed potatoes, sauerkraut and sausages on plates.
Serve mashed potatoes sprinkled with parsley and garnished.