Combine cornbread crumbs, bread cubes, salt, pepper, and thyme in a large bowl.
Sauté celery, mushrooms, and onion in butter until tender; add to cornbread mixture, stirring well. Stir in next 5 ingredients.
Spoon dressing into a lightly greased 13- x 9- x 2-inch baking pan. Bake at 375° for 1 hour or until browned. Cut into squares, and spoon on Creamed Chicken.