In the casserole melt half the butter over a medium heat and add the potatoes, leeks and fennel, stir-fry for 4 - 5 minutes. Lift out with a slotted spoon onto a plate.
Melt the rest of the butter in the casserole, stir in the flour and cook gently for 1 minute. Remove the casserole from the heat and gradually stir in the hot vegetable stock. Place back onto the heat and bring to the boil, stirring all the time. Return the potatoes, leeks and fennel to the stock.
Add the bay leaves and chilli flakes and simmer for 6 - 7 minutes until the potatoes begin to soften.
Stir in the asparagus, peas and the creamed corn, bring back to a simmer and continue to cook for 5 - 6 minutes until all of the vegetables are tender.
Remove the bay leaves. Using a potato masher or the back of a spatula lightly crush some of the vegetables to thicken the soup.
Stir in 100ml (3½floz) of the crème fraiche with most of the chopped parsley and season the soup to taste with salt and black pepper.
Serve the soup piping hot with a spoon of the remaining crème fraiche, sprinkled with the remaining chopped parsley.
It is important to season the soup at the end of stage 5 as the level required will depend on the type of stock used, as well as personal taste. Frozen peas can be used if fresh are not available.