Melt half the butter and cook the onion and garlic gently for 5 minutes in a covered saucepan without colouring. Stir in the flour and cook gently for a minute, stirring.
Gradually add the stock, stirring all the time. Add half the mushrooms and parsley. Cover, bring to the boil and simmer gently for 10-15 minutes until the vegetables are tender. Cool a little , then puree in a liquidiser.
Saute the remaining mushrooms in the remaining butter for 5 minutes until they begin to brown then add to the pureed soup. Simmer gently for 3 minutes then stir in the cream and check seasoning.