Wash the cauliflower, remove the stalk and cut into small florets.
Wash, peel and chop the carrots. Bring water to a boil and add cauliflower and carrots. Peel and chop the onion and add to it. Cook everything until the vegetables are soft (about 20 minutes).
Put the vegetables in the blender or puree with the hand blender.
Put butter in a saucepan and melt, then add the flour and stir well to make a roux. Slowly pour in the chicken stock while stirring and bring to the boil briefly. Then add the pureed vegetables and bring to the boil again. Stir the cream into the soup and finally season with salt, pepper and nutmeg to taste.