01 - Preheat the oven to 350°F. Line an 8-inch square baking pan with parchment paper, allowing overhang for easy removal.
02 - Cream together butter and sugar until light and fluffy. Incorporate flour and salt, mixing until crumbly dough forms.
03 - Press dough evenly into the prepared pan. Bake 18 to 20 minutes until lightly golden. Cool completely.
04 - Heat sugar in saucepan over medium heat, stirring until melted and amber-colored. 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 microwaving in short bursts, stirring until smooth.
07 - Spread melted chocolate evenly over chilled caramel. Refrigerate at least 30 minutes until firm.
08 - Remove bars from pan using parchment overhang. Cut into 16 bars with a sharp knife, wiping blade between cuts for clean edges.