Preheat your oven to 350°F (175°C). Line the baking pan with parchment paper, leaving some overhang for easy removal later.

In a food processor, crush the pistachios until finely ground. Combine with graham cracker crumbs, sugar, and melted butter in a mixing bowl. Mix until well combined.

Press the crust mixture firmly into the bottom of the prepared pan to create an even layer. Bake for 10 minutes, then remove from the oven and let cool slightly.

In another mixing bowl, using an electric mixer, beat the softened cream cheese and sugar until smooth and creamy. Add eggs, one at a time, mixing well after each addition. Stir in vanilla extract and sour cream until fully combined.

Pour the cheesecake filling over the cooled crust. Bake for 30 minutes, or until the center is set but slightly jiggles. Turn off the oven, crack the door, and let the cheesecake cool in the oven for 30 minutes.

While the cheesecake cools, prepare the blackberry topping. In a small saucepan, combine blackberries, sugar, lemon juice, cornstarch, and water. Cook over medium heat, stirring gently until the blackberries break down and the mixture thickens, about 5-7 minutes. Remove from heat and let cool slightly.

Once the cheesecake is cooled, spread the blackberry topping evenly on top. Refrigerate for at least 3 hours or until fully chilled and set.

Lift the cheesecake out of the pan using the parchment overhang and cut into 12 bars.