01 - Line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - Using a double boiler, gently melt the chopped chocolate and butter together, stirring occasionally until smooth and glossy.
03 - Remove from heat and, if desired, fold in chopped nuts and dried fruit.
04 - Pour the melted chocolate mixture into the prepared pan, spreading evenly with a spatula.
05 - Sprinkle flaky sea salt on top, if preferred.
06 - Refrigerate for at least 40 minutes, or until fully set and firm.
07 - Lift the set chocolate out using parchment overhang, cut into large chunks with a sharp knife, and store in an airtight container at a cool room temperature or refrigerate.