
In a large pan melt the butter and gently fry the garlic and onions until soft. Add the mushrooms and stir fry for another 2 minutes or until just starting to soften.
Sprinkle flour over the mushrooms and stir in well. Some flour may start to stick to the base of the pan at this point, but don't worry.
Next, add the wine and scrape up any bits of flour. As the wine reduces it will mix with the flour and start to thicken.
As the wine thickens start to add the milk a little at a time whilst continually stirring. The gradual additions of milk and continual stirring will prevent any lumps forming and will create a silky, smooth white sauce.
Once all the milk is added continue to stir and allow to simmer for a couple of minutes to ensure the flour is cooked out and the sauce is fully thickened.
Next add parmesan, dijon mustard, creme fraiche and seasoning to the sauce and stir in well.
Finally add cooked spaghetti to the pan and stir to coat in the sauce, then top with extra parmesan and fresh parsley and serve.