01 - Preheat oven to 350°F (175°C). Line a 9x9 inch (22x22 cm) baking pan with parchment paper, leaving some overhang.
02 - In a medium bowl, whisk together the flour, cocoa powder, cardamom, baking powder, and fine sea salt. Set aside.
03 - Combine the chopped chocolate and cubed butter in a heatproof bowl over a saucepan of simmering water (double boiler), stirring until smooth and glossy. Remove from heat and cool slightly.
04 - Add the granulated sugar to the melted chocolate mixture, whisking until fully incorporated. Beat in eggs one at a time, then stir in the vanilla extract and rose water if using.
05 - Gently fold the dry ingredient mixture into the wet ingredients until just combined. Avoid overmixing for optimal texture.
06 - Fold in 1/2 cup chopped pistachios and chocolate chips or chunks if desired.
07 - Pour batter into prepared pan, leveling the surface. Sprinkle remaining pistachios evenly over the top.
08 - Bake for 28–32 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Do not overbake.
09 - Let cool completely in the pan on a wire rack. Sprinkle with flaky sea salt before slicing into squares.