Wash the kale thoroughly and remove any thick stems, tearing or cutting leaves into bite-sized pieces.

If using frozen kale, separate leaves before adding to the pot.

In a large heavy pot over medium heat, melt the goose fat, lard, or butter.

Add the finely chopped onions and cook for a few minutes until soft, fragrant, and lightly golden.

Gradually add the kale, allowing each handful to wilt before adding more and stirring continuously to coat.

Add the mustard, sugar, black pepper, and a small pinch of salt, then pour in the broth.

Nestle the Kassler and smoked pork belly into the kale, pushing them down slightly.

Cover and simmer on low heat for 45 to 60 minutes, stirring occasionally and adding more broth if necessary.

Place the Pinkelwurst and Mettwurst on top of the kale after the initial cooking time.

Cover again and cook for another 30 to 40 minutes, avoiding boiling.

Check the consistency of the kale and simmer uncovered if too thin.

Meanwhile, boil the potatoes in salted water until tender and serve whole or halved.

Adjust the seasoning of the kale before serving with more pepper, mustard, or sugar if needed.

Let the pot sit off heat for about 5 to 10 minutes, then slice the Kassler and serve alongside the kale and potatoes, spooning some of the liquid over the dish.