Place the mussels in a large bowl of cold water. Use a small knife to remove any barnacles and pull away the beard. Discard any mussels that are damaged or won’t close when tapped.
Heat the oil in a large saucepan set over medium heat and add the bacon and cook, stirring occasionally, until brown and crisp. This will take 5-6 minutes. Using a slotted spoon, transfer the cooked bacon to a plate lined with paper towels. Set bacon aside.
Add the shallots and garlic to the saucepan and cook, stirring frequently, until the shallots soften. Increase the heat and add the sprigs of thyme and cider. Bring to the boil. Add the mussels and cover tightly. Allow the mussels to cook for 3-4 minutes, shaking the pan from time to time to ensure they cook evenly. Discard any that have not opened.
With a slotted spoon remove the mussels from the sauce and divide them between 4 serving bowls.
Remove the thyme from the sauce and whisk in the crème fraiche and Dijon mustard and simmer. Check for seasoning, remember the cooking liquid and bacon can be salty so be cautious! Pour the finished sauce over the mussels, sprinkle on the bacon and chopped parsley. Serve with crusty bread and a sliced tomato and red onion salad.