01 - Preheat oven to 340°F. Line the bottom of a 9-inch springform pan with parchment paper and grease the sides.
02 - Combine graham cracker crumbs, melted butter, chopped pistachios, and sugar in a bowl. Press firmly into the base of the prepared pan.
03 - Bake the crust for 10 minutes until set. Remove from oven and let cool completely.
04 - Beat cream cheese and sugar in a large bowl until smooth and fluffy. Add yogurt or sour cream and vanilla extract, mixing well.
05 - Add eggs one at a time, mixing gently after each addition just until incorporated.
06 - Fold in ground pistachios and cornstarch until fully combined.
07 - Pour filling over cooled crust. Tap pan gently to release air bubbles. Bake for 45 minutes until edges are set and center still jiggles slightly.
08 - Turn off oven, open door slightly, and let cheesecake cool inside for 1 hour.
09 - Cool to room temperature, then refrigerate for at least 4 hours or preferably overnight.
10 - Whip heavy cream with powdered sugar to soft peaks. Spread over chilled cheesecake and sprinkle with chopped pistachios before serving.