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 to create an even base. Chill in the refrigerator for 10 minutes.
03 - In a heatproof bowl, melt chopped chocolate and heavy cream together over simmering water or in 30-second microwave intervals, stirring until smooth. Stir in vanilla extract.
04 - Pour the melted chocolate mixture evenly over the chilled biscuit base, spreading with a spatula.
05 - Sprinkle nuts, mini chocolate chips, and sea salt over the chocolate layer, if desired.
06 - Refrigerate the assembled bar for at least 1 hour or until firm.
07 - Lift the bar from the pan using the parchment paper overhang, then cut into 12 squares. Serve chilled or at room temperature.