Melt butter in a heavy saucepan over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add milk; cook over medium heat, stirring constantly, until sauce is thickened and bubbly. Add 1/4 cup plus 2 tablespoons cheese, salt, celery salt, and pepper. Cook, stirring constantly, until cheese melts.
Place cabbage wedges in a shallow baking dish. Pour sauce over cabbage. Sprinkle remaining 1/4 cup cheese and breadcrumbs over top. Bake at 350° for 10 minutes or until cheese melts. Sprinkle with chopped parsley and serve.