Wash the mussels in a colander to remove any dirt and grit. Pick through them, removing any stringy ‘beards’ from the shells. If any of the mussels are slightly open, tap them on the work surface to see if they close (which means they are still alive) and discard any that remain open. Melt the butter in a large heavy-based saucepan. Sauté the spring onions and garlic over a high heat for 2 minutes before pouring in the cider. Add the thyme, bay leaf, crushed pepper, saffron strands, fish stock pot and the mussels. Cover and cook for 4-5 minutes or until the mussels start to open. Add the cream, squeeze in the juice of ½ lemon and stir in the parsley. Divide the mussels between bowls. Pour over the sauce and any spring onions left in the pan. Serve with crusty bread to mop up the juices.