Melt the butter in a saucepan, add the leeks, potato, and celery, and cook over gentle heat for 10-15 minutes. Pour the stock over and add most of the cauliflower florets, reserving a few for garnish. Bring the contents of the saucepan to a boil and cook until the vegetables are tender. Allow to cool slightly.
Meanwhile, cook the reserved cauliflower florets in boiling salted water until just al dente. Drain and keep warm.
Puree the soup in a blender or food processor, then return to the pan and add cream to give the desired consistency. Season with salt, pepper, and nutmeg. Gently reheat the soup, then stir in the reserved florets. Serve with some crisply fried croutons.
© 1999 Jennifer Paterson and Clarissa Dickson Wright estate. All rights reserved.