Place the potatoes, carrots and stock in a large saucepan and bring to the boil.
Meanwhile, melt the knob of butter in a shallow saucepan and add the pinch of salt, mushrooms and garlic, tossing until well coated. When mushrooms have softened, lower the heat and add the cream. Do not let it boil, just heat through slowly.
When the potatoes and carrots are soft right through use a potato masher and mash them in the stock. DO NOT DRAIN.
Lower the heat of the now mashed carrots and potato and pour in the creamy mushrooms and mix well. Season with oregano and warm through.
Serve with buttered bread and enjoy.
50g butter mixed with a clove of crushed garlic, 1/2 teaspoon of oregano and 1/2 teaspoon of basil spread onto fresh white bread goes very well with this soup.