Preheat your oven to 350°F (175°C) and grease or line an 8x8 inch baking dish with parchment paper.

Prepare the brownie batter according to the package instructions. Pour it into the baking dish and bake for 20–25 minutes, or until the center is just set. Remove from the oven and let cool slightly.

While the brownies are baking, melt the butter in a saucepan over medium heat. Add the knafeh pastry and toast it, stirring frequently, until golden and crisp, about 5–7 minutes. Remove from heat and stir in the pistachio spread until fully combined.

Once the brownies have cooled slightly but are still warm, spread the pistachio knafeh mixture evenly over the brownie layer and press it down gently.

Sprinkle the chopped pistachios evenly over the knafeh layer and press them in slightly.

To make the ganache, heat the heavy cream in a small saucepan over medium heat until it just starts to simmer. Pour it over the semisweet chocolate in a heatproof bowl and let sit for 1–2 minutes, then stir until smooth.

Pour the ganache over the pistachio layer and spread it out evenly. Finish with a sprinkle of flaky sea salt on top.

Refrigerate the brownies for at least 1 hour to allow the ganache to set. Slice into 9 bars and serve.