In a medium bowl, cream butter and sugar until fluffy. Carefully blend in flour until mixture is evenly crumbly. Be careful not to over mix or shortbread will become tough. Press into 9 inch square pan and bake for 20 minutes. Set aside to cool.
Cut caramels into small pieces and melt in saucepan with water and cream on medium heat, stirring occasionally until completely melted. Spread caramel onto cooled shortbread and set aside to cool.
Chop dark chocolate into small pieces and melt in heatproof bowl in microwave or on stove until completely melted. Remove from heat and stir in butter until mixture is smooth and silky. Spread on top of caramel layer and chill for 20 minutes in fridge or for 1 hour at room temperature. Cut into 1inch squares to serve.