This creamy soup has a very subtle taste - the secret is to use fish stock. It is especially nice topped with a few drops of truffle oil which you can buy at delis.
In a saucepan, simmer the cauliflower with the fish stock until very tender.
Remove from heat and blend with a stick blender until creamy. Return to heat and add the cream and spring onion. Add salt and pepper to taste and simmer a few more minutes.
Serve hot in bowls, drizzles with a few drops of truffle oil if you like.