Pre-heat the oven to 180°C /fan 160°C/ gas mark 4.
Melt the butter in a large wide bottomed pan.
Add the bacon, leek, celery and carrot and fry gently for 5 minutes.
Stir in the bay leaf and parsley and cook for a further 10 minutes until the vegetables are soft.
Add in the crème fraiche, cream cheese, dijon, half of the cheddar cheese and black pepper and stir together until a smooth sauce has formed. Cook gently until just bubbling then remove from the heat.
Chop the parsnips and potatoes into equal sizes then place into a large saucepan and fill with cold water. Bring to the boil then turn down to a simmer for 15-20 minutes until soft. Then drain.
Melt the butter in the same saucepan the potatoes were cooked in.
Pour the potatoes and parsnips into the saucepan and mash well. Add a little salt.
To assemble, place the cubed salmon into the bottom of a large baking dish and pour the sauce over the top in an even layer.
Scoop the potato on top and spread out with the back of a fork roughing up the surface but make sure the sauce is fully covered.
Scatter the remaining cheddar cheese over the top and place in the oven for 30 minutes until bubbling and the cheese has turned golden.