Cream butter and sugar until smooth. Add egg yolk, mix well. Sift flour with cinnamon and salt. Add flour mixture to butter mixture. Mix lightly but thoroughly, use hands. Spread in even layer on medium size cookie sheet. Smooth surface. Beat egg white slightly. Spread egg white over top of cookie. Sprinkle with nuts. Press nuts into dough. Bake 275 degrees 45 - 50 minutes Cut while hot.