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 the mixture firmly into the bottom of the prepared pan to form an even layer. Chill for 10 minutes in the refrigerator.
03 - Place chopped chocolate and heavy cream in a heatproof bowl. Melt over simmering water or in 30-second microwave intervals, stirring until smooth. Mix in vanilla extract.
04 - Pour the melted chocolate mixture over the chilled biscuit base and spread evenly using a spatula.
05 - Sprinkle chopped nuts, mini chocolate chips, and a pinch of sea salt over the chocolate layer if desired.
06 - Refrigerate for at least 1 hour or until the chocolate is firm.
07 - Lift the bars out using the parchment paper overhang. Cut into 12 squares with a sharp knife. Serve chilled or at room temperature.