01 - Preheat oven to 340°F. Line the bottom of a 9-inch springform pan with parchment paper and grease the sides thoroughly.
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. Bake for 10 minutes until set. Let cool completely on a wire rack.
03 - In a large bowl, beat cream cheese and granulated sugar with an electric mixer until completely smooth and fluffy, about 2-3 minutes. Add Greek yogurt (or sour cream) and vanilla extract, mixing until well combined.
04 - Add eggs one at a time, beating on low speed and mixing just until incorporated after each addition. Do not overmix to prevent cracks.
05 - Fold in ground pistachios and cornstarch until evenly distributed throughout the batter.
06 - Pour the filling over the cooled crust. Tap the pan gently against the counter several times to release trapped air bubbles. Bake for 45 minutes or until edges are set and center still jiggles slightly when gently shaken.
07 - Turn off the oven and crack the door open slightly. Let the cheesecake cool inside for 1 hour to prevent cracking. Remove and cool to room temperature, about 1 additional hour.
08 - Refrigerate for at least 4 hours or preferably overnight until completely set and firm.
09 - Whip heavy cream with powdered sugar until soft peaks form. Spread over chilled cheesecake and sprinkle with chopped pistachios just before serving.