Preheat the oven to 325°F and grease or line a muffin tin for 10 cups.
Prepare the brownie batter according to the box instructions (eggs, oil, water/milk). Divide the batter evenly between the muffin cups, filling each about 3/4 full.
Bake the brownies for 18 to 22 minutes, or until they are crispy around the edges, shiny on top, and puffed up.
While the brownies bake, heat a pan over medium heat and add the neutral oil. Add the chopped kataifi and cook, stirring often, until the strands turn golden and crispy.
Transfer the toasted kataifi to a plate lined with a paper towel to drain any excess oil. Then transfer it to a small bowl and combine with the pistachio paste until well mixed.
Once the brownies come out of the oven, let them cool for about 20 minutes. Use the back of a spoon or the opposite end of a muddler to gently press down the center of each brownie to create a cup.
Spoon the pistachio kataifi filling into each brownie cup to fill it up.
Add the chopped chocolate to a bowl and pour the heavy cream over it. Microwave in 30-second intervals on low power, mixing between each interval, until smooth and glossy, about 2 to 3 intervals total.
Spoon the chocolate ganache over the pistachio filling.
Finish with a sprinkle of chopped pistachios on top and let the ganache set before serving.