01 - Line an 8x8 inch square baking pan with parchment paper, ensuring an overhang on the sides for effortless removal. This will assist in lifting the finished bars.
02 - Gently melt the finely chopped dark or semi-sweet chocolate with unsalted butter. Achieve this either using a double boiler method (a heatproof bowl set over a saucepan of simmering water) or by carefully heating in a microwave in 30-second intervals, stirring until completely smooth and unified.
03 - Pour half of the melted chocolate mixture into the prepared pan, spreading it evenly across the bottom. Refrigerate for approximately 15 minutes, or until this initial chocolate layer is firmly set.
04 - While the chocolate chills, combine the unwrapped soft caramels and heavy cream in a small saucepan. Cook over low heat, stirring constantly, until the caramels are fully melted and the mixture is smooth and uniform.
05 - Carefully spread the warm caramel filling evenly over the chilled chocolate layer. Evenly sprinkle the roughly chopped mixed nuts on top of the caramel, gently pressing them down to adhere. If desired, lightly sprinkle with flaky sea salt for enhanced flavor.
06 - Pour the remaining melted chocolate mixture over the nut and caramel layer, spreading it meticulously to ensure full and even coverage.
07 - Refrigerate the pan for a minimum of 30 minutes, or until the entire chocolate bar slab is completely firm and set throughout.
08 - Using the parchment paper overhang, carefully lift the solid chocolate bar slab from the pan. With a sharp knife, cut into individual bars of your desired size. Serve at room temperature or lightly chilled.