01 - Pulse digestive biscuits in a food processor until fine crumbs form, or place in a sealed zip-top bag and crush with a rolling pin.
02 - Pour melted butter over the biscuit crumbs and stir until the mixture resembles wet sand and holds together when pressed.
03 - Transfer the crumb mixture into an 8-inch springform pan and press firmly across the bottom in an even layer. Refrigerate for 20 minutes to firm up.
04 - In a large mixing bowl, combine softened cream cheese, pistachio paste, powdered sugar, and vanilla extract. Beat with an electric mixer on medium speed until completely smooth and lump-free.
05 - In a separate chilled bowl, whip the cold heavy cream to stiff peaks using an electric mixer or whisk, being careful not to overwhip.
06 - Gently fold the whipped cream into the pistachio mixture in three additions, using a spatula and wide sweeping motions to preserve as much air as possible.
07 - Pour the filling over the chilled biscuit base and spread evenly with an offset spatula, smoothing the surface.
08 - Cover the pan tightly with plastic wrap and refrigerate for at least 4 hours, preferably overnight, until the filling is firm and set throughout.
09 - Remove the cheesecake from the springform pan, scatter chopped pistachios and white chocolate shavings over the top if desired, slice into wedges, and serve chilled.