01 - Pulse the digestive biscuits in a food processor until fine crumbs form. Alternatively, place them in a sealed zip-top bag and crush with a rolling pin. Pour in the melted butter and mix until the crumbs are evenly coated and resemble wet sand.
02 - Transfer the buttery crumb mixture into an 8-inch springform pan. Press firmly and evenly across the bottom using the back of a spoon or the base of a measuring cup. Refrigerate for 20 minutes to allow the crust to firm up.
03 - In a large mixing bowl, combine the softened cream cheese, pistachio paste, powdered sugar, and vanilla extract. Beat with an electric mixer on medium speed until completely smooth, scraping down the sides as needed.
04 - In a separate chilled bowl, whip the cold heavy cream using an electric mixer or whisk until stiff peaks hold their shape when the beaters are lifted. Be careful not to over-whip.
05 - Gently fold the whipped cream into the pistachio cream cheese mixture in three additions, using a large spatula and slow sweeping motions. Preserve as much volume and air as possible for a light, mousse-like texture.
06 - Spoon the filling over the chilled biscuit base, spreading it into an even layer. Smooth the surface with an offset spatula, working from the center outward.
07 - Cover the pan tightly with plastic wrap and refrigerate for a minimum of 4 hours, though overnight chilling yields the best results. The cheesecake should be firm to the touch and hold its shape when sliced.
08 - Just before serving, scatter the chopped pistachios and any optional toppings over the surface. Run a thin knife around the edge of the pan, release the springform ring, and slice into 8 even portions.