Melt the butter in a large saucepan and add the sliced onions; put a lid on the pan and sweat the onions for about 15 to 20 minutes, until they are soft but are not brown. Add the crème fraiche and mix well
2
Add the stock and the cider to the pan and bring to the boil before simmering for 5 to 10 minutes until the soup has thickened slightly. Season to taste with salt and pepper
3
Meanwhile, heat the grill to high and place the crumbled or sliced cheese on top of the toasted slices of bread; place the cheese topped croutons on a tray and place under the grill until the cheese has melted and is bubbling
4
Ladle the soup in warm soup bowls and place a grilled Cheddar crouton on top. Serve immediately