01 - Crush the digestive biscuits into fine crumbs using a food processor or by placing them in a sealed bag and rolling over with a rolling pin. Combine the crumbs with melted butter, stirring until evenly coated and the mixture resembles wet sand.
02 - Press the buttery 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.
03 - In a large mixing bowl, beat together the softened cream cheese, pistachio paste, powdered sugar, and vanilla extract until completely smooth and creamy with no lumps remaining.
04 - In a separate chilled bowl, whip the cold heavy cream using an electric mixer or whisk until stiff peaks form, being careful not to overwhip.
05 - Gently fold the whipped cream into the pistachio cream cheese mixture using a spatula, using light sweeping motions to preserve as much air and volume as possible.
06 - Spoon the airy pistachio filling over the chilled biscuit base, spreading it out evenly and smoothing the surface with a spatula.
07 - Cover the springform pan and refrigerate the cheesecake for at least 4 hours, or preferably overnight, until the filling is firm and fully set.
08 - Just before serving, scatter the roughly chopped pistachios over the top of the cheesecake along with any optional toppings. Release from the springform pan, slice into wedges, and serve chilled.