Reduce oven heat to 320F.
In a medium bowl, add chopped pistachios, powdered sugar, and melted butter and combine.
In a large mixing bowl, mix well all of the cheesecake ingredients: cream cheese, mascarpone, heavy whipping cream, sugar, eggs, flour, and corn starch.
Add half of the pistachio mixture into the springform pan over the base of the phyllo dough. Using your hands gently press to the bottom. Pour the cheesecake mixture into the springform pan. Set aside.
Cut three sheets of phyllo dough into an 8 inch circle,using the base of the springform pan for reference. Sprinkle each layer with1/2 tbsp melted butter and 1/2 tsp sugar and stack on top of each other. Pressthe other half of the pistachio mixture on the top of the phyllo dough circles,add carefully on top of the cheesecake mixture. Prepare 12 square layers ofphyllo dough, repeating the initial process of butter and sugar between eachlayer. Cut the stack into an 8 inch circle, and cut 8 wedges into the dough.Place each wedge on top of the cheesecake. Bake the cheesecake for 60 minutes,then cover the top loosely with aluminum foil (if it’s already brown and flaky,otherwise no need) before baking for an additional 10-15 minutes.
Remove from the oven, let cool at room temperature. Refrigerate at least 4 hours or overnight.