Cream butter in a large mixing bowl; gradually add sugar, beating until light and fluffy. Add egg yolk, almond paste and almond extract; beat until well blended. Stir in flour. Spread mixture into a 33x23x5cm or similar sized baking tin.
Beat egg white until foamy; brush over entire surface of base and sprinkle with almonds. Bake for 35 minutes or until lightly browned. Cool thoroughly and cut into 5cm squares. Store in airtight containers.