01 - Preheat oven to 340°F. Line the bottom of a 9-inch springform pan with parchment paper and grease the sides with butter.
02 - Combine crushed graham crackers, melted butter, chopped pistachios, and sugar in a bowl. Press mixture firmly into the base of the prepared pan. Bake for 10 minutes until lightly golden. Allow to cool completely.
03 - Beat cream cheese and granulated sugar in a large bowl until 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, mixing on low speed after each addition just until blended. Avoid overmixing to prevent cracks.
05 - Fold in ground pistachios and cornstarch until fully incorporated and no dry streaks remain.
06 - Pour filling over cooled crust. Tap pan gently against counter several times to release trapped air bubbles.
07 - Bake for 45 minutes or until edges are set and center still jiggles slightly when gently shaken.
08 - Turn off oven and crack door open slightly. Let cheesecake cool inside for 1 hour to prevent sudden temperature change.
09 - Remove from oven and cool to room temperature, about 1 hour. Refrigerate for at least 4 hours or overnight until completely set.
10 - Whip heavy cream with powdered sugar until soft peaks form. Spread over chilled cheesecake and sprinkle with chopped pistachios before serving.