Select the kale and wash thoroughly. Blanch in plenty of boiling salted water in portions for about 3 minutes. Drain, chop coarsely
Peel and chop the onions. Heat clarified butter in a pot. Brown the onions in it. Add kale and pour in about 1 1/2 l water. Bring to the boil and stir in broth. Cover and cook for about 1 hour.
Peel, wash and cut the potatoes into pieces. Add the sausages and potatoes to the kale 30 minutes before the end of the cooking time and cook until done
If necessary, roast the mustard seeds briefly in a pan without fat and add them. Season kale with salt, pepper and sugar. Halve the sausages if necessary.