Peel and chop the vegetables, cut the onions into rings. Bring all the ingredients for the brew to the boil and let it simmer for a few minutes (you can also prepare the broth, then it pulls through nicely).
Clean the mussels and add them to the boiling stock. Turn the heat down a bit. Cover and cook for approx. 5-10 minutes. As soon as the mussels are open, remove them from the pot and serve immediately.
Serve as a side dish with brown bread with butter.