In a food processor, pulse graham cracker crumbs until finely ground. In a mixing bowl, combine the crumbs with melted unsalted butter and granulated sugar until well mixed. Press this mixture firmly into a 9-inch springform pan to create an even crust. Freeze the crust for 30 minutes to set while you prepare the filling.

In a chilled mixing bowl, whip cold heavy whipping cream using an electric mixer until stiff peaks form, which usually takes about 3-5 minutes. Cover the bowl and refrigerate the whipped cream to keep it cool while you prepare the cheesecake filling.

In a separate large bowl, beat full-fat cream cheese and confectioners sugar together until light and fluffy, about 2-3 minutes. Gradually add the instant pistachio pudding mix, vanilla extract, almond extract, and sour cream, mixing until smooth and well combined.

Gently fold the chilled whipped cream into the pistachio mixture using a spatula, taking care not to deflate the airiness. Continue folding until no streaks remain, and the mixture is smooth and creamy.

Pour the cheesecake filling over the prepared crust in the springform pan, smoothing the top with a spatula for an even finish. Cover the pan with cling film and refrigerate it to chill for at least 6-8 hours, ideally overnight.

When ready to enjoy, remove from refrigerator, loosen the edges with a knife, and release the springform pan. Slice into servings and garnish each slice with whipped cream and a sprinkle of chopped pistachios.