Preheat your oven to 335°F and line one 8x8-inch brownie pan with parchment paper. Make sure the parchment paper hangs over two opposite sides of the pan for easy removal.
Measure the butter (113g) and the dark chocolate (60g) into a large heatproof bowl, and melt in the microwave using 30 seconds increments.
Add the cocoa powder (45g), then pour over the boiling water and mix until smooth.
Mix in the sugar (250g), followed by the eggs (2).
Mix the flour (60g) and the baking powder (1/8 teaspoon) then add it to the chocolate mixture.
Fold in 1/2 cup of the pistachio cream but not all the way, count three folds.
Fold the chocolate chips
Pour the batter into your prepared pan, use an off set spatula to spread it into an even layer.
Dot the batter with the remaining 1/2 cup of pistachio cream, then use a toothpick to swirl it. Sprinkle the chopped pistachios on top.
Bake for 25-28 minutes, over the middle oven rack, until the a toothpick comes out from the center of the pan with a few very moist (like clumped batter) crumbs.
Remove from the oven and set aside to set until completely cool, about 2-3 hours.
Use the access parchment paper to remove the brownie from the pan onto a slicing board, and slice to 9, 12, or 16 bars.
Store in an airtight container for up to 5 days, or freeze wrapped ina plastic wrap and a freeze sealed bag for up to 3 weeks.