01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - Cream butter and sugar until light and fluffy. Stir in flour and salt until a crumbly dough forms.
03 - Press dough evenly into the prepared pan. Bake 18 to 20 minutes until lightly golden. Let cool completely.
04 - Heat sugar in a medium saucepan over medium heat, stirring until melted and amber. Add butter and stir until melted. Slowly add cream and salt, stirring until smooth. Simmer 1 to 2 minutes, then remove from heat and cool slightly.
05 - Pour caramel evenly over cooled shortbread. Refrigerate at least 45 minutes until set.
06 - Melt chocolate and butter together in a heatproof bowl over simmering water or in short microwave bursts. Stir until smooth.
07 - Evenly spread melted chocolate over chilled caramel. Refrigerate at least 30 minutes until firm.
08 - Lift bars from pan using parchment. Cut into 16 bars with a sharp knife, wiping blade between cuts for clean edges.