01 - Preheat oven to 340°F. Line the bottom of a 9-inch springform pan with parchment paper and grease the sides thoroughly with butter.
02 - Combine graham cracker crumbs, melted butter, chopped pistachios, and sugar in a medium bowl. Press the mixture firmly into the base of the prepared pan, ensuring an even layer.
03 - Bake the crust for 10 minutes until lightly golden. Remove from oven and set aside to cool completely while preparing the filling.
04 - In a large mixing bowl, beat cream cheese and granulated sugar with an electric mixer on medium speed until completely smooth and fluffy, about 2-3 minutes.
05 - Mix in Greek yogurt (or sour cream) and vanilla extract until fully incorporated and smooth.
06 - Add eggs one at a time, beating on low speed just until blended after each addition. Avoid overmixing to prevent cracks.
07 - Fold in ground pistachios and cornstarch until evenly distributed throughout the batter.
08 - Pour the filling over the cooled crust. Tap the pan gently on the counter to release any air bubbles. Bake for 45 minutes until edges are set and center still slightly jiggles.
09 - Turn off the oven and crack the door open slightly. Let cheesecake cool inside for 1 hour to prevent sudden temperature changes.
10 - Remove from oven and cool to room temperature, about 1 hour. Refrigerate for at least 4 hours or overnight until completely set.
11 - Just before serving, whip heavy cream with powdered sugar until soft peaks form. Spread over chilled cheesecake and sprinkle with chopped pistachios.