Mix graham cracker crumbs, melted butter, and sugar until it resembles wet sand. Press firmly into the bottom of a parchment-lined 9x13 inch pan. Freeze for 15 minutes while you prepare the filling.

Beat 1 cup cold heavy cream in a large bowl until stiff peaks form, about 3-4 minutes. Set aside in the refrigerator.

Beat cream cheese and powdered sugar until completely smooth and fluffy, about 2 minutes. Add vanilla and remaining 1/2 cup unwhipped cream, beat until incorporated.

Gently fold the whipped cream into the cream cheese mixture in two additions until no streaks remain. Spread half the filling over the chilled crust. Dollop pistachio cream in spoonfuls over the surface, then swirl lightly with a knife. Spread remaining cheesecake filling on top and smooth the surface. Refrigerate while you make the kataifi.

Preheat oven to 350F. Toss chopped kataifi with melted butter until coated. Spread on a baking sheet and bake for 8-10 minutes, stirring once, until deeply golden and crispy. Cool completely. Sprinkle evenly over the cheesecake layer and press gently to adhere.

Heat 3/4 cup cream until steaming but not boiling. Pour over chopped chocolate, let stand 2 minutes, then stir until glossy and smooth. Stir in corn syrup if using. Pour over the kataifi layer, tilting the pan to create an even coating. Refrigerate at least 4 hours or overnight until completely set. Lift out using parchment overhang and cut into bars with a hot, dry knife.