Preheat oven to 350°F (175°C) and position rack in the middle position. Line an 8×8 inch (20×20cm) light-colored aluminum baking pan with parchment paper leaving at least 2 inches (5cm) of overhang on two opposite sides.

Pulse 200g of graham crackers in a food processor until fine, uniform crumbs form — approximately 15 to 20 one-second pulses. Transfer to a large mixing bowl. Add 85g melted butter, 25g granulated sugar, and a pinch of fine sea salt. Stir with a fork until every crumb is evenly coated and the mixture holds together when pressed between fingers. Reserve 2 tablespoons of the unbaked crumb mixture in a small bowl for the optional crumble garnish.

Press the crumb mixture firmly and evenly into the prepared pan using the flat bottom of a measuring cup, pressing well into the corners. Bake at 350°F (175°C) for 10 to 12 minutes until the edges are set and the surface looks dry and lightly golden. Transfer to a wire rack and cool completely — approximately 45 minutes to 1 hour — before adding any filling.

Beat 340g of softened full-fat block cream cheese alone on medium speed for 2 full minutes until completely smooth. Scrape the bowl. Add 65g pistachio paste, 120g sifted powdered sugar, ½ teaspoon vanilla extract, and a pinch of fine sea salt. Beat on medium speed for 1 minute until fully combined. Scrape the bowl.

In a separate clean cold bowl, whip 120ml of cold heavy whipping cream on high speed to stiff peaks — approximately 2 to 3 minutes. Fold the whipped cream into the pistachio cream cheese mixture in two additions using gentle bottom-upward strokes — approximately 20 strokes per addition. Pour onto the cooled crust, spread evenly with an offset spatula, and refrigerate for a minimum of 45 minutes until the center feels firm when gently pressed.

Beat 225g of softened full-fat block cream cheese alone on medium speed for 2 full minutes until completely smooth. Scrape the bowl. Add 80g sifted powdered sugar, 1 teaspoon vanilla extract, and a pinch of fine sea salt. Beat on medium speed for 1 minute. Scrape the bowl. In a separate clean cold bowl, whip 120ml of cold heavy whipping cream to stiff peaks. Fold into the vanilla cream cheese mixture in two additions. Spoon carefully over the set pistachio layer and spread gently with an offset spatula. Refrigerate for another 45 minutes to 1 hour until firm.

In a medium saucepan over medium heat, combine 300g blackberries, 80g granulated sugar, and 15ml lemon juice. Cook stirring occasionally until blackberries have broken down completely and the mixture is bubbling — approximately 8 to 10 minutes. Strain through a fine mesh sieve, pressing firmly to extract all liquid and pulp. Discard seeds and skin. Whisk together 7g cornstarch and 30ml cold water until smooth. Add the cornstarch slurry to the strained blackberry liquid in the saucepan. Cook over medium heat stirring constantly until the mixture thickens and reaches a full rolling boil — approximately 2 to 3 minutes. Cook for exactly 1 minute more at a full boil stirring constantly. Remove from heat and cool to room temperature — approximately 65–70°F (18–21°C) — approximately 20 to 30 minutes.

Confirm the vanilla layer is firm at the center. Pour the cooled blackberry gel over the set vanilla layer in a slow steady stream from the center outward. Tilt the pan to distribute evenly and use an offset spatula to spread to the corners. Cover loosely with plastic wrap without touching the gel surface. Refrigerate for a minimum of 4 hours — overnight is recommended.

Use the parchment overhang to lift the fully set slab onto a cutting board. Dip a sharp chef's knife in hot water, wipe completely dry, and press straight down in a single motion — repeat for every cut. Make 3 evenly spaced cuts in one direction, rotate, make 3 more cuts to yield 16 bars. Garnish with chopped pistachios and fresh blackberries immediately before serving, or scatter reserved crust crumble across the gel surface for the crumble garnish variation.