Clean and quarter the fresh mushrooms. Cut celery and carrots into 1/2 inch pieces. Place oil in a large pot. Add chopped onions; cook over low heat for about 10 minutes until wilted. Add garlic, thyme and bay leaf. Add mushrooms and cook for 20 minutes over medium heat, stirring. Add the barley, celery, carrots and broth. Season with salt and pepper to taste and the nutmeg. Bring to a boil, reduce heat to medium low and simmer 25 to 30 minutes or until barley and vegetables are tender. Skim off any foam that rises to the top. Remove bay leaf. Stir in the parsely just before serving piping hot. Clean mushrooms with damp towel never wash in water.