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