1. Preheat oven to 180C. Trim chicken and cut into 10 portions.
2. Place chicken, onion, spices and salt into 8-cup capacity ovenproof dish. Cover with water. Bake 30 minutes. Remove chicken. Strain liquid into bowl, reserving 2 cups. Melt half the butter in frying pan. Add mushrooms, cook until soft. Add garlic, cook 2 minutes. Transfer to bowl.
3. Melt remaining butter in pan. Add flour, cook 2 minutes. Gradually add reserved liquid, stir until smooth. Bring to boil. Remove from heat, stir in cream, mustard and mushrooms.4. Return chicken and sauce to dish. Sprinkle with combined cheese, breadcrumbs and parsley. Bake 30 minutes.
Storage time: Prepare this dish up to one day ahead. Cover, refrigerate.