Cream butter and brown sugar together until light. Beat in egg yolk and vanilla. Sift together flour and cinnamon; stir into creamed mixture. Pat dough into ungreased 15 x 10 x 1-inch baking pan. Brush with egg white; sprinkle with nuts and lemon peel and additional cinnamon if you like. Press nuts lightly into surface. Bake in 350° oven for 18 to 20 minutes. Cut into diamonds; cool and remove from pan. Freeze any extra cookies in moisture-vapor wrap. Makes 4 dozen.