Pre-heat oven to 180 degrees C. Grease a Swiss roll tin.
Cream butter, 1/2 cup of the sugar and egg yolks until well blended. Add flour and mix well. Pat dough evenly into bottom of prepared tin and bake for 15-20 minutes or until lightly browned.
Remove tin from oven (but leave oven on). Let cool for 5 minutes then spread with the jam. Beat egg whites and salt until stiff but not dry. Carefully fold in remaining sugar and the chopped nuts.
Gently spread on top of the jam, making sure to seal edges and corners. Return to oven for 25 minutes or until golden brown. Cut into bars while still warm. May be stored airtight at room temperature up to a week. May also be frozen. Defrost covered at room temperature.