Preheat your oven to 350°F (175°C). In a bowl, combine all-purpose flour, sugar, and salt. Cut in the cold butter until coarse crumbs form. Add egg yolk and ice water, mixing until dough forms. Press into a greased baking pan and pre-bake for 15-20 minutes until golden.

Cook fresh blackberries and sugar in a saucepan over medium heat for 5-7 minutes until juices are released. Mix in cornstarch and lemon juice, cooking 1-2 minutes until thick. Let cool slightly.

In a clean bowl, whisk together brown sugar, baking powder, and salt. Cut in cold butter until crumbly. Add egg and vanilla, stirring until combined. Fold in pistachios.

Spread blackberry filling evenly over the crust. Sprinkle pistachio topping covering the filling entirely. Bake for 30-35 minutes until golden and bubbly.

Allow to cool in the pan for 1-2 hours, then lift out and slice into squares.