1 Rinse kale, trim, remove tough stems and cut into strips. Peel onions and chop finely. Cut chestnuts into small pieces. Melt butter in a hot pot and sauté onions until soft. Add chestnuts and kale and cook briefly. Add broth and simmer covered for 15-20 minutes. Remove kale and set aside. Add cream, stir into soup and puree everything with an immersion blender. Add kale again. Slice mettwurst, add to the pot and let simmer for 4-5 minutes in the soup. Season to taste with salt, pepper, nutmeg and sugar. Serve in bowls.