Wash the mussels and discard any that are broken and do not close when tapped.
Put a splash of olive oil in a frying pan and cook the leeks on a medium heat with the garlic and cook until tender, take out and reserve. In the same pan turn the heat up high and heat up the pan until red hot. Put the mussels in with the cider and put the lid on and cook until the shells have opened. Take the mussels out using a colander making sure you catch the cooking liquor. Add the leeks and cream to the cooking liquor and pour over the mussels.
To serve - sprinkle with roughly chopped parsley and serve with crusty bread.