Preheat oven to 180ºC F. In a large bowl, combine flour, sugar and salt; cut in margarine until crumbly. stir in 1 beaten egg. Press evenly in a 9x13 inch pan. Bake for 25 minutes. Meanwhile, in medium bowl, beat sweetened condensed milk, remaining egg and flavoring; stir in nuts. Sprinkle chocolate chips evenly over the prepared crust. Top with the nut mixture. Bake for 25 minutes more or until lightly brown. Cool. Cut into bars. Store tightly covered at room temperature. Makes 24 36 bars.