01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, ensuring overhang for easy removal.
02 - Cream together butter and sugar until light and fluffy. Incorporate flour and salt until crumbly dough forms.
03 - Press dough evenly into pan. Bake for 18 to 20 minutes until lightly golden. Cool completely before proceeding.
04 - Heat sugar in medium saucepan over medium heat, stirring constantly until amber. Add butter and stir until melted. Gradually add heavy 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 base. Refrigerate at least 45 minutes until set.
06 - Melt chocolate and butter together in a heatproof bowl over simmering water or microwave in short bursts, stirring until smooth.
07 - Spread melted chocolate evenly over chilled caramel layer. Refrigerate 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.