Grease 2 quart casserole dish and preheat oven to 350. Cook onion and carrots in butter, stir in flour and seasonings. Increase heat amd add milk and chicken broth. Bring to a boil stirring constantly. Cook 5 minutes, add chicken, peas/corn, mushrooms and cook for 5 more minutes. Pour into dish and cover with jiffy mix (make with milk and egg). Cook for 45 minutes or until cornbread is browned.