01 -
Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan or line it with parchment paper for easy removal of the bars. In a food processor, pulse the pistachios until finely chopped but not powdered. In a large bowl, combine the ground pistachios, flour, sugar, baking powder, and salt. Add the softened butter and mix until the dough comes together. Stir in the oats. Press the crust mixture evenly into the prepared baking pan. Bake for 15-18 minutes, or until lightly golden and firm. Remove from the oven and set aside.
02 -
In a medium bowl, mash the blackberries with a fork or potato masher to release their juice. Stir in the sugar, eggs, vanilla extract, flour, salt, and baking powder until fully combined. Pour the blackberry filling over the baked pistachio crust and spread it evenly. Sprinkle the remaining pistachio crumble mixture over the blackberry filling, covering it as evenly as possible.
03 -
Return the pan to the oven and bake for 30-35 minutes, or until the filling is set and the top is golden brown.
04 -
Allow the bars to cool completely in the pan on a wire rack before slicing into squares. This will help the bars set and prevent them from falling apart. Slice into 16 squares and serve. You can garnish with additional pistachios or a dusting of powdered sugar for an extra touch of elegance.