In a large saucepan bring the stock to boiling point, then add the mussels. Pop the lid on the pan, turn the heat down and let them cook for 2 minutes, shaking the pan as they cook.
Add the other ingredients, giving the mussels a quick stir and let cook for 1 more minute before dishing up the mussels into bowls and pouring the stock over them.
Serve with a chunk of baguette to mop up the juices