Wash the kale thoroughly and remove thick, tough stems. Tear or cut the leaves into bite-sized pieces and ensure they’re clean.

For frozen kale, separate as much as possible before adding it to the pot.

Heat the goose fat, lard, or butter in a large, heavy pot over medium heat. Add the finely chopped onions. Cook for a few minutes until they are soft and lightly golden, releasing a delicious aroma.

Gradually add the kale, allowing each portion to wilt slightly before adding more. Stir continuously to coat all the leaves, ensuring even cooking and flavor infusion.

Stir in the mustard, sugar, black pepper, and a small amount of salt if using. Pour in the broth and mix well. The kale should be moist, simmering gently without being submerged.

Place the Kassler and smoked pork belly into the kale, pressing them down lightly. Their smoky juices will enrich the dish as it cooks, adding depth.

Cover the pot and let it simmer on low heat for 45 to 60 minutes. Stir occasionally to prevent sticking and add more broth if it starts to dry out.

After the initial cooking, add the Pinkelwurst and smoked Mettwurst. Gently press them into the kale and cover again, cooking on low heat for another 30 to 40 minutes.

Gently stir the kale and check its consistency. If it's too thin, let it simmer uncovered for a few minutes. If too dry, add a splash of broth and stir well.

While the kale is finishing, boil the potatoes in salted water until tender. Drain well and serve them whole, halved, or browned in butter for a lovely contrast.

Just before serving, taste the kale. Adjust seasoning with more pepper or mustard if necessary. Let it sit off the heat for a few minutes before serving.

Slice the Kassler as desired and serve the kale along with the sausages and potatoes. Spoon some of the savory liquid over the dish.