Drain a little water from already cooked potatoes, add to it a crushed mass of onions and mushrooms. Pour the cream and connect the blender to work. We grind the soup with it to the state that you like best - you can smooth it in a smoothie, you can stop when you still feel small lumps of mushrooms and potatoes. We put the soup again on the stove and bring to a boil (do not let it boil !!!). We try and bring to taste.