Melt the butter in a deep saucepan and add the bacon cubes. Cook over a medium to high heat for 5 minutes. Wash the leeks and slice into thin rings. Add the leeks to the bacon and cook gently until soft.
While the bacon is cooking, de-beard the mussels.Discard any that do not close immediately when tapped. Place the mussels, thyme and cider in a bowl.
Once the bacon is crisp and golden brown, drain any excess fat from the pan. Return the bacon to the heat and add the bowl of mussels, cider and thyme. Cover with a tight fitting lid. Shake the pan and cook over a high heat for 2 to 3 minutes. The mussels should open and be plump and juicy after this time. Cooking them for longer will cause them to become tough. Finally, roughly chop the parsley, add to the pot and stir through.
Serve the mussels in a large bowl, discarding any that have not opened in the cooking process. You should not need to season this dish as the bacon and mussels are quite salty. Serve in a deep bowl with plenty of crusty bread to mop up the delicious juice.
«Store mussels in the fridge covered only with a damp kitchen towel as covering them with cling film will kill them.»