Preheat your oven to 350°F (175°C). In a food processor, combine all-purpose flour, ground pistachios, powdered sugar, and salt. Pulse in cold unsalted butter until the mixture resembles coarse crumbs. Add the egg yolk and a splash of ice water, blending until a cohesive dough forms. Press the dough into a lined 8x8 or 9x9 inch pan, poke with a fork, and bake for 18-20 minutes until golden. Allow it to cool completely.

In a mixing bowl, beat room-temperature cream cheese until it’s fluffy and smooth. Gradually add powdered sugar, pistachio paste, vanilla extract, and a pinch of salt, mixing until fully incorporated. In a separate bowl, whip heavy cream to soft peaks, then gently fold it into the cream cheese mixture to maintain the lightness. Spread this luscious pistachio cream over the cooled crust, ensuring an even layer, and refrigerate to set.

In a saucepan over medium heat, combine fresh blackberries, granulated sugar, and lemon juice. Stir occasionally until the blackberries soften, releasing their juices—this should take about 5-7 minutes. In a small bowl, mix cornstarch with water to create a slurry, then add it to the fruit mixture. Continue to cook until the compote thickens, roughly 2-3 minutes. Allow it to cool slightly before spreading it evenly over the pistachio layer.

Sprinkle chopped pistachios on top of the blackberry compote. Cover the pan with plastic wrap and chill in the refrigerator for at least 4 hours, but preferably overnight to let the flavors meld beautifully. This resting time is crucial for achieving the perfect balance of sweetness and tartness.

Once chilled and set, use the parchment paper to lift the Blackberry Pistachio Dream Bars out of the pan. With a sharp knife, cut them into squares for serving. For clean cuts, wipe the knife between slices.