01 - Line the base of an 8-inch springform pan with parchment paper, ensuring it lies flat against the bottom.
02 - Pulse the graham crackers in a food processor until fine crumbs form. Transfer to a bowl, add the melted butter and sugar, and stir until the mixture resembles wet sand and holds together when pressed.
03 - Firmly press the crumb mixture into an even layer across the bottom of the prepared pan. Place in the refrigerator to set while you prepare the filling.
04 - If using gelatin sheets, submerge them in a bowl of cold water for 5 minutes until pliable. If using powdered gelatin, sprinkle it evenly over 3 tablespoons of cold water and let it bloom for 5 minutes.
05 - Gently warm the bloomed gelatin in a small saucepan over low heat just until fully dissolved and liquid. Remove from heat and let cool slightly for 2 to 3 minutes.
06 - In a large mixing bowl, beat the softened cream cheese, pistachio paste, powdered sugar, vanilla extract, and lemon juice with an electric mixer until completely smooth and free of lumps.
07 - In a separate chilled bowl, whip the cold heavy cream with an electric mixer until soft peaks form — the cream should hold its shape briefly when the beaters are lifted but still appear billowy.
08 - Gently fold the whipped cream into the cream cheese mixture using a spatula, working in three additions to preserve as much air as possible.
09 - Scoop about 3 tablespoons of the filling into the dissolved gelatin and stir to temper. Pour this mixture back into the main filling and fold gently until fully incorporated and uniform.
10 - Pour the filling over the chilled crust and use a spatula to smooth the surface into an even layer. Tap the pan gently on the counter to release any trapped air bubbles.
11 - Refrigerate the cheesecake for a minimum of 4 hours, or preferably overnight, until the filling is firm and set throughout.
12 - Release the springform pan ring and transfer the cheesecake to a serving plate. Scatter chopped pistachios over the top and garnish with fresh berries or mint leaves if desired. Slice with a warm, clean knife and serve chilled.