Heat the oven to 200°C (400°F)
Cook the macaroni to al-dente according to package and then set aside with some butter so it does not stick.
Take a large pot and melt the butter, whisk down the flour. Heat up the milk in the microwave and add to the mixture. Whisk in the crème fraiche.
Bring to a boil and then reduce heat and let it simmer for 5 min
While it simmers you can heat up a small pan with a tbsp of butter and then add the breadcrumbs. Let it soak in the butter and toast a bit (careful not to burn it), set aside.
Shred the cheese then add to the pot while stirring
Simmer a few minutes until all cheese has melted
Take it off the heat and toss with the macaroni until everything is coated
Grease an oven pan and pour in the mac & cheese. Sprinkle the buttered breadcrumbs over it and bake for 20 min