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. Transfer the crumbs to a bowl and pour in the melted butter, stirring until the mixture resembles wet sand and holds together when pressed.
02 - Press the crumb mixture firmly and evenly into the bottom of an 8-inch springform pan, using the back of a measuring cup or spoon to compact it. Refrigerate for 20 minutes to allow the base 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 the mixture is 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 form — the cream should hold its shape when the beaters are lifted without collapsing.
05 - Gently fold the whipped cream into the pistachio-cream cheese mixture in three additions, using a large spatula and slow, sweeping motions. Fold just until incorporated to preserve maximum volume and lightness.
06 - Spoon the filling over the chilled crust, 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 at least 4 hours, though overnight chilling yields the best texture and cleanest slices.
08 - Just before serving, sprinkle the chopped pistachios and any optional toppings over the surface. Release the springform pan ring, slice into 8 portions with a sharp knife dipped in hot water, and serve immediately.