01 - Line a 9-inch springform pan with parchment paper. Combine biscuit crumbs, melted butter, and brown sugar until fully incorporated. Press mixture firmly and evenly into the base of the pan. Refrigerate for 20 minutes to set.
02 - In a saucepan, melt butter, brown sugar, and golden syrup over medium heat. Blend in sweetened condensed milk, stirring constantly. Continue to cook, stirring, for 8 to 10 minutes until the caramel thickens and turns golden. Optionally, stir in sea salt. Pour the caramel over the chilled base, smooth evenly, and refrigerate for 1 hour.
03 - Using an electric mixer, beat softened cream cheese with caster sugar until smooth. Gently fold in the lightly whipped heavy cream and vanilla extract. Spread mixture over the fully set caramel, smoothing the top. Chill for at least 4 to 5 hours, or overnight for optimal texture.
04 - Heat heavy cream until steaming but not boiling. Pour over chopped dark chocolate in a heat-resistant bowl. Let stand for 2 minutes, then add butter and stir until the ganache is glossy and completely smooth. Cool slightly, then spread evenly over the cheesecake layer. Refrigerate for 1 to 2 hours to allow the ganache to set.
05 - Before serving, run a knife dipped in hot water around the cake’s edge to loosen. Release from the springform pan. Slice with a clean, warm knife for defined layers and serve chilled.