In a saucepan Fry onions, and celery until soft. Add garlic for 5 minutes. Add mushrooms and mix well with the above ingredients and cover. Fry mushrooms until liquid is gone. Add cream and cook until it comes to a boil. Add parsley and simmer for about 10 minutes. Disolve flour in water until there are no lumps (a plastic container with a lid lets you shake until no lumps) Add flour/water mixture to mushrooms and simmer for 10 minutes to thicken.