01 - Pulse the digestive biscuits into fine crumbs using a food processor, or place them in a sealed zip-top bag and crush with a rolling pin.
02 - Combine the biscuit crumbs with the melted butter, stirring until the mixture is evenly moistened and resembles wet sand.
03 - Press the crumb mixture firmly and evenly into the bottom of an 8-inch springform pan. Refrigerate for 20 minutes to allow the base to firm up.
04 - In a large mixing bowl, beat the softened cream cheese, pistachio paste, powdered sugar, and vanilla extract together until smooth and free of lumps.
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, using a spatula and sweeping motions to preserve as much volume as possible.
07 - Spoon the filling over the chilled biscuit base and smooth the surface evenly with a spatula.
08 - Cover the pan tightly and refrigerate for at least 4 hours, or preferably 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.