First separate the florets of the cauliflower from the hard stalk (this can be kept and grated for a salad).
Now you need to separate the florets themselves into very tiny pieces.
Then in a medium saucepan bring the stock and bay leaf to simmering point, throw in the little pieces of cauliflower and simmer for about 6 minutes, or until they are just cooked but still have some ‘bite’. Lift them out with a draining spoon and keep them on one side. Pour in the milk now and add the potatoes, then simmer gently without a lid until the potatoes are soft – about 10 minutes.
Next run the soup through a sieve, or liquidise it, and return it to the saucepan.
Now return the cauliflower to the saucepan and reheat gently, adding a squeeze of lemon juice, some seasoning, and a scraping of nutmeg.