01 - Line an 8x8 inch baking pan with parchment paper, leaving overhang for easy removal.
02 - Combine crushed biscuits, melted butter, and sugar until uniform. Press firmly into the bottom of the pan. Chill in refrigerator for 10 minutes.
03 - Place chopped chocolate and heavy cream in a heatproof bowl. Melt over simmering water or microwave in 30-second intervals, stirring until smooth. Stir in vanilla extract.
04 - Pour melted chocolate mixture evenly over chilled biscuit base, spreading with spatula.
05 - Sprinkle nuts, mini chocolate chips, and sea salt over chocolate layer, if desired.
06 - Refrigerate for at least 1 hour until firm.
07 - Lift bars using parchment overhang. Cut into 12 squares with a sharp knife. Serve chilled or at room temperature.