01 - Pulse the digestive biscuits in a food processor until fine crumbs form. Alternatively, place them in a sealed zip-top bag and crush thoroughly with a rolling pin.
02 - Pour the melted butter over the biscuit crumbs and stir until the mixture is evenly moistened. Press firmly and evenly into the bottom of an 8-inch springform pan. Refrigerate for 20 minutes to allow the base to firm up.
03 - In a large mixing bowl, beat the softened cream cheese, pistachio paste, powdered sugar, and vanilla extract together using an electric mixer until completely smooth and lump-free.
04 - In a separate chilled bowl, whip the cold heavy cream to stiff peaks using an electric mixer or whisk.
05 - Gently fold the whipped cream into the pistachio-cheese mixture in three additions, using a spatula and sweeping motions to preserve as much volume and air as possible.
06 - Spoon the filling over the chilled biscuit base and spread evenly. Smooth the surface with an offset spatula.
07 - Cover the pan tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until the cheesecake is fully set and firm to the touch.
08 - Just before serving, scatter the chopped pistachios and any optional toppings over the surface. Release the springform ring, slice into 8 portions, and serve chilled.