01 - Line an 8 x 8 inch square baking pan with parchment paper, ensuring overhang on the sides for easy removal.
02 - Combine chocolate and butter in a heatproof bowl over simmering water or microwave in 30-second intervals, stirring until smooth.
03 - Pour half of the melted chocolate into the prepared pan, spreading evenly. Refrigerate for 15 minutes until set.
04 - Heat caramels and heavy cream in a saucepan over low heat, stirring continuously until smooth and fully melted.
05 - Spread the caramel over the chilled chocolate layer evenly. Sprinkle chopped nuts over caramel and gently press them in. Optionally, add flaky sea salt.
06 - Pour remaining melted chocolate over the nut layer and spread to cover completely.
07 - Refrigerate the assembled layers for at least 30 minutes until fully firm.
08 - Lift the set slab from the pan using parchment overhang and cut into 12 bars with a sharp knife. Serve at room temperature or slightly chilled.