Heat the butter in a sauce pan. Put 1/2 cup of mushroom pieces into it. Saute for a while and remove from the pan. Put the onion and garlic in the remaining butter and saute well.
Boil the remaining mushroom pieces in water with coriander leaves and salt for 10 minutes. When it becomes cool, grind the contents.
Mix the corn flour with milk. Add this to the mushroom solution. Place it in fire and boil for 3 minutes. Remove from fire and add the sauted mushroom pieces and pepper powder and stir. Decorate the soup with coriander leaves.