In a saucepan, combine mushrooms, onions, parsley, garlic, tarragon, vegetable stock and wine. Bring to a boil over medium heat. Reduce heat and boil gently, stirring often, for about 20 minutes or until mushrooms
In a small bowl, mash flour with butter until blended.
Whisk into saucepan until blended. Boil gently, stirring constantly, for about 5 minutes or until sauce is thickened. Season with salt and pepper to taste.