Start by crushing the digestive biscuits or graham crackers into fine crumbs—use a food processor or seal in a plastic bag and crush with a rolling pin. Mix the crumbs with melted butter until evenly coated. Press this mixture firmly into the base of a springform pan, creating an even layer. Chill in the fridge for about 15 minutes to set.
While the crust chills, break the dark chocolate into small pieces and melt it gently in a heatproof bowl set over simmering water or microwave in 30-second bursts, stirring until smooth and glossy. Be careful not to overheat or seize the chocolate.
In a mixing bowl, beat the softened cream cheese with superfine sugar until smooth and creamy—about 2 minutes. Add vanilla extract if using, mixing just to combine.
Gently fold the melted chocolate into the cream cheese mixture, using a spatula, until fully incorporated and silky in appearance.
Whip the chilled heavy cream to soft peaks—listen for a gentle swoosh and watch it hold a soft curl when you lift the whisk. Carefully fold the whipped cream into the chocolate and cream cheese mixture in three additions, using a spatula to keep the mixture light and airy.
Pour the luscious filling over the chilled crust, smoothing the top with a spatula. Tap the pan gently on the counter to remove any air bubbles and ensure an even surface. Cover loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until fully set and firm.
Once set, run a warm knife around the edges of the cheesecake before unlocking and removing the springform sides. For clean slices, dip the knife in hot water and wipe dry between cuts.
Decorate with cocoa powder, chocolate shavings, or fresh berries as you like. Slice with a sharp, warm knife and serve chilled for that silky, decadent experience.
