Preheat the Oven: Preheat the oven to 390°F (200°C). Take a sheet of phyllo dough spread ½ tablespoon of butter on it and sprinkle 1 teaspoon of powdered sugar. Add an additional sheet of dough and repeat until 6 sheets overlap. Line a 20cm springform mold with the dough, letting it hang over the edges. Pierce the bottom with a fork and bake for 5 minutes. Remove from oven and let cool. Reduce oven temperature to 320°F (160°C).

Prepare Nut Mixture: Mix ground pistachios, powdered sugar, and melted butter in a bowl.

Make Cheesecake Filling: In a large mixing bowl, blend the cream cheese, mascarpone, cream, powdered sugar, eggs, flour, and cornstarch until smooth.

Assemble Base: Spread half of the pistachio mixture over the cooled phyllo base. Pour the cheesecake filling over the top.

Prepare Top Layers: Cut three more phyllo sheets into 8-inch circles. Brush each with melted butter, sprinkle with powdered sugar, and stack them. Spread the remaining pistachio mixture on top and carefully place this stack on the cheesecake filling.

Bake: Prepare 12 more phyllo sheets using the butter and sugar method, stacking them as before. Cut into an 8-inch circle, then into 8 wedges. Arrange the wedges on top of the cheesecake. Bake for 60-75 minutes or until set and golden. Cover with foil if browning too quickly.

Cool and Chill: Remove cheesecake from the oven, let cool at room temperature, then refrigerate for at least 4 hours or overnight.

Prepare Syrup: In a saucepan, combine water, sugar, and lemon slices. Bring to a boil, then simmer for 10-12 minutes. Let cool until warm.

Serve: Pour half of the warm syrup over the baklava layers and around the edges. Let sit for 5-10 minutes before slicing. Serve with extra syrup on the side.