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