Preheat your oven according to the instructions on the brownie mix package, typically to 350°F (175°C). Prepare your baking pan by greasing or lining it with parchment paper.

In a large mixing bowl, combine the brownie mix, eggs, water, and oil. Stir until well-blended and smooth. Pour mixture into prepared baking pan and bake for 20-25 minutes.

Remove the brownie pan from the oven and allow it to cool in the pan on a wire rack for 30-45 minutes.

In a separate large bowl, beat together softened cream cheese and powdered sugar until smooth and creamy, about 2-3 minutes.

Add the heavy cream and pistachio extract to the mixture. Continue mixing on medium-high speed for about 3-4 minutes until light and fluffy.

Carefully pour the cheesecake mixture over the cooled brownie base and spread evenly with a spatula.

Sprinkle the top with chopped pistachios.

Cover with plastic wrap and refrigerate for at least 4 hours or overnight.

Once set, lift the bars out of the pan using the parchment paper and cut into squares.