Prepare the crust: Crush biscuits into fine crumbs, mix with melted butter and ground pistachios. Press firmly into the bottom of a 23 cm springform pan. Chill for 15 minutes.
Make the filling: In a large bowl, beat cream cheese, ricotta, and sugar until smooth. Add eggs one at a time, mixing well. Fold in pistachio paste, sour cream, vanilla, and lemon zest.
Bake the cheesecake: Preheat oven to 160°C. Pour filling over the crust. Place the pan in a larger tray with hot water (water bath). Bake for 50–55 minutes until the center is just set.
Chill the cheesecake: Turn off oven, crack door slightly, and let cheesecake cool gradually. Then refrigerate for at least 4 hours or overnight.
Prepare topping & serve: Whip heavy cream with powdered sugar. Spread over cooled cheesecake and garnish with chopped pistachios. Slice and serve cold.