Boil a large volume of water in a pot, immerse the raw sauerkraut in it for 10 minutes, then drain and squeeze it in a cloth.
Peel and finely chop the onions, then melt them in a casserole with the goose fat. Add half of the sauerkraut, the smoked bacon, the pork shoulder, the cloves, the juniper berries, the bay leaves, the rest of the sauerkraut, and the wine. Cover the casserole and let simmer on low heat for 1 hour.
Meanwhile, peel the potatoes and steam them for 20 minutes. Set aside.
Add the Montbéliard sausages to the casserole, ensuring they are covered with sauerkraut, and continue cooking. After 10 minutes, add the Strasbourg sausages and cook for another 10 minutes. Just before serving, add the potatoes to warm them in the casserole.