Combine butter, brown sugar, and egg yolk. Beat until creamy. Stir in flour, salt, and cinnamon. Mix well. Spread dough into lightly greased jelly roll pan. Beat egg white until foamy. Stir in powdered sugar. Spread egg-sugar mixture over batter. Sprinkle with chopped nuts. Bake 30 to 35 minutes. While hot, cut into bars. Remove from pan and cool on rack.