Preheat oven to 325 degrees F. Lightly grease an 8 or 9 inch baking pan.
To make shortbread: in a medium bowl, beat butter and sugar 5 to 8 minutes or until light and fluffy. Stir in flour to make a smooth dough. Knead dough in bowl 8 to 10 strokes. Pat out dough evenly in bottom of greased pan. Prick dough with a fork. Bake in preheated oven 35 to 40 minutes or until golden. Cool in pan or a wire rack.
To make topping: in a medium saucepan over medium heat, combine butter, sugar, corn syrup and condensed milk. Cook, stirring, until mixture comes to boil. Boil 5 to 7 minutes or until mixture is toffee-colored and thickened, stirring occasionally. Cool slightly, spread over cooled shortbread in pan. Let stand until cool.
In a small heavy saucepan over very low heat, melt chocolate and shortening. Cook, stirring until smooth. Cool slightly. Spread chocolate over cooled toffee. Let stand until chocolate is set. Cut into bars and remove from pan.
Ingredients for shortbread:
Ingredients for topping:
