In a mixing bowl, cream butter, sugar and salt till fluffy. Gradually
beat in flour. Spread into a greased 13 x 9 inch pan. Bake at 350º for
16-20 minutes or till lightly browned
In a microwave safe bowl, combine condensed milk and chocolate chips. Microwave, uncovered, on high for 1-2 minutes or until chips are melted; stir until
smooth. Stir in extract. Spread over the shortbread.