Clean the cauliflower well. Dip it in a bowl of boiled salt water and steam. Keep the boiled water aside.
Remove the thick portions of the cauliflower. Keep aside some flowers of the cauliflower and grind the remaining soft portions.
Heat the butter in a sauce pan. Saute the flour in it. Add the boiled water slowly into it. (If needed some more water can be added.) It should be about 3 3/4 cup of water. Add the ground cauliflower into the sauce pan.
Beat the egg yolk and cream together in a vessel. Put a little soup into this and beat well. Transfer the whole thing into the sauce pan. Add the flowers kept aside earlier into this. Heat the soup. Do not allow to boil. Serve hot by adding pepper powder and chopped coriander leaves.