For the mariniere:
Add a drizzle of oil or a cube of butter into a hot pan. Add the chopped shallots, celery, onion and leek.
Give it a stir and let the vegetables soften in the pan for a few minutes.
Crush the garlic cloves using the flat side of a knife and the palm of your hand and add them to the pan.
Add a few sprigs of thyme and the bay leaves (no need to separate the thyme leaves from the stalk as this is a rough and ready dish!).
Soften the onions in the pan for approximately 2 more minutes, until the onions are translucent but not too soft.
Add the wine and the water to the pan, and leave the bouillon to simmer for 15 to 20 minutes.
While your mariniere is simmering, prep your mussels, removing as much of the stringy ‘beard’ as possible. Be sure to discard any mussels that are already open or cracked.
Put a clean and empty pan on the stove with the heat on and leave to stand for 30 seconds on high heat. Add mussels , leave for 20 seconds, then add 3 ladles of the pre-made mariniere sauce. Put the lid on and steam until all the mussels are open ( about 3-4 minutes).