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. Incorporate flour and salt until a crumbly dough forms.
03 - Press dough evenly into prepared pan and bake for 18 to 20 minutes until edges are lightly golden. Cool completely.
04 - Heat sugar over medium heat in a saucepan, stirring constantly until it melts and turns amber. Add butter and stir until melted. Slowly add heavy cream and salt, stirring to a smooth consistency. Simmer for 1 to 2 minutes, then remove from heat and cool slightly.
05 - Pour caramel evenly over cooled shortbread base. Refrigerate for at least 45 minutes until set.
06 - Combine chocolate and butter in a heatproof bowl over simmering water or microwave in short bursts, stirring until smooth.
07 - Evenly spread melted chocolate over chilled caramel layer. Refrigerate for at least 30 minutes until firm.
08 - Lift bars from pan using parchment overhang. Cut into 16 bars with a sharp knife, wiping blade between cuts for clean edges.