In a small saucepan, combine blackberries, sugar, and lemon juice. Simmer on low heat for about 10 minutes until the blackberries soften. Strain the mixture through a fine mesh sieve and let the reduction cool.

In a food processor, pulse together the flour, ground pistachios, sugar, and cold butter until the mixture is crumbly. Press this mixture firmly into a lined 8×8 baking pan.

Bake the crust in a preheated oven at 350°F (175°C) for 12–15 minutes, or until it turns lightly golden.

In a mixing bowl, beat the softened cream cheese and sugar together until smooth. Add the eggs and vanilla extract, mixing until everything is fully combined.

Pour the cream cheese filling over the baked crust. Spoon the cooled blackberry reduction on top, and use a toothpick to swirl it gently into the filling.

Bake everything together for 30–35 minutes, or until the edges are set and the center remains slightly jiggly.

Allow the bars to cool completely, then refrigerate for at least 4 hours before slicing into squares.

Before serving, garnish each piece with crushed pistachios and fresh blackberries.