Heat oven to 300 degrees. Line a 10 X 15 cookie sheet with aluminum foil. Coat with cooking spray.
In a large bowl, with an electric mixer on medium, beat butter and sugar until fluffy. Beat in egg yolk, almond extract and salt. Gradually beat in flour.
Press dough evenly in prepared pan with your hands. Beat egg white in small bowl until foamy. Brush evenly over dough, then sprinkle with almonds.
Bake 35 to 40 minutes or until gently brown. Let cool. Lift foil out of pan. Cut into 2" squares with serrated knife.