Position a rack in the middle of the oven and preheat to 325°F. Coat a 9" x 9" baking dish with cooking spray and line it with parchment paper, leaving some hanging over on two sides.
In a large bowl, mix the brownie batter according to the instructions on the package. Pour the mixture into the prepared dish and spread the top evenly.
Bake the brownies for 35 to 40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Allow the brownies to cool.
In a large skillet over medium-low heat, melt the butter. Add the kataifi and cook, stirring frequently. Reduce the heat if the kataifi starts to darken too much. Cook until it turns a deep golden color, about 15 to 18 minutes, then take it off the heat.
Stir in the tahini and 1 1/4 cups plus 2 tablespoons of the pistachio cream. Let this mixture cool while the brownies bake and cool. Once cooled, spread the kataifi mixture over the brownies.
Place the chocolate chips in a medium heatproof bowl. In a medium pot, heat the cream over medium heat until it lightly bubbles around the edges. Pour the hot cream over the chocolate and let it sit for 2 minutes, then whisk until fully melted and smooth.
Pour the ganache over the kataifi layer. Drizzle the remaining 2 tablespoons of pistachio cream over the ganache and use a toothpick to create swirls without disturbing the kataifi. Top with chopped pistachios.
Lift the brownies out of the dish using the parchment overhang and place them on a cutting board. Cut into squares.
Notes
Prep time and cook time are not specified. The recipe yields a batch of brownies that can be cut into squares.