Place the butter, flour and sugar in a food processor and process until it begins to bind together. Press the mixture into a greased and floured 9 inch square pan and smooth the top. Bake in a preheated oven 350 degrees for 20-25 minutes or until golden.
Meanwhile, make the filling. Place the butter, sugar, syrup and condensed milk in a saucepan and heat gently until the sugar has melted. Bring to a boil and simmer for six to eight minutes, stirring constantly, until the mixture becomes very thick. Pour over the shortbread base and leave to chill in the refrigerator until firm.
Melt the chocolate and cool. Then spread over the caramel. Chill in the refrigerator until set. Cut the shortbread into 12 pieces with a sharp knife and serve.