Heat the butter in a large pan. Add the onion and garlic and leave to cook on a medium heat for 2 or 3 minutes, until they become soft and clear.
Whilst the onion and garlic are softening, chop the cauliflower as finely as possible. Add the chopped cauliflower to the onions and pour in the boiling water. Bring back to the boil. Reduce the heat and simmer for 30 minutes.
When the cauliflower is tender, stir then taste the soup, add the cheese and adjust the seasoning, if you think it needs it.
Whizz the soup with the cream in a liquidiser.