Peel and finely dice the onions, fennel and garlic. Peel the potato and cut into small dice. Cut the leeks into quarters lengthways and then dice. Finely chop the chives.
De-beard the mussels and check that they are alive, discarding any that are not.
Melt the butter in a saucepan and sweat the onions, fennel and leeks at a low heat until they are soft. Add the potato and garlic and cook for a further minute. Add the white wine to the pan and reduce by this half. Add enough fish stock to cover the vegetables and bring to the boil. When boiling, reduce the heat to a simmer.
Whilst the soup is cooking, place the mussels in a separate pan, add a splash of water and cover with a lid. Cook over a high heat until all of the mussels are open (about 3 minutes). Once cooked, keep the mussels warm.
When the soup is cooked and the vegetables are completely soft, place the soup in a blender and blitz with the double cream. Check the seasoning and grate in some nutmeg.
To serve: Fill the soup bowl with the soup, add a few open mussels and finish with a sprinkling of chives.
«Check if any open mussels are alive by tapping them on your chopping board. If they close they are alive and good to cook.»