Take a large saucepan with a lid (big enough to steam the mussels) and melt the butter over a high heat. Add the shallots, bacon lardons and leeks, and fry for 1 minute.
Tip in the garlic, half the parsley, and the bay leaf and simmer for a few seconds. Add the mussels, cider, calvados, and cream; bring to the boil and cover.
Lower the heat and cook, shaking the pan occasionally, until the mussels open. Cook for about 3 minutes and then remove from the heat.
Strain the mussels, reserving the liquor. Pick all of the meat from the mussels and place into an earthenware dish. Bring the reserved liquor to simmering point and stir in the cheese until sauce has thickened.
Pour the sauce over the mussels and garnish with the remaining chopped parsley and a grinding of cracked pepper.
Meanwhile set the oven to 400F and slice both baguettes in half vertically. Slice, cutting only three quarters the way through the bread (as you would when making conventional garlic bread).
Place the remaining ingredients into a food processor and blend together until smooth. Spread this mixture between the slices of baguette. Wrap each piece in kitchen foil and bake for 5 minutes. Serve hot with the camembert mussels.