01 - Pulse the digestive biscuits in a food processor until fine crumbs form, or place them in a sealed bag and crush with a rolling pin.
02 - Pour the melted butter over the biscuit crumbs and stir until the mixture is evenly coated and resembles wet sand.
03 - Transfer the crumb mixture into an 8-inch springform pan and press firmly into an even layer across the bottom. Refrigerate for 20 minutes to firm up.
04 - In a large mixing bowl, beat the softened cream cheese, pistachio paste, powdered sugar, and vanilla extract together until completely smooth and creamy.
05 - In a separate chilled bowl, whip the cold heavy cream to stiff peaks using an electric mixer or whisk.
06 - Gently fold the whipped cream into the pistachio-cream cheese mixture in two additions, preserving as much volume and air as possible.
07 - Spoon the filling over the chilled biscuit base and spread evenly with a spatula, smoothing the top surface.
08 - Cover the pan tightly and refrigerate for at least 4 hours, or ideally overnight, until the cheesecake is fully set and firm.
09 - Just before serving, scatter the chopped pistachios and any optional toppings over the surface. Release the springform ring, slice into wedges, and serve chilled.