Preheat oven to 350° F (180° C). Butter the sides of an 8- by 8-inch baking dish. Dust the sides with flour and tap out excess. Line the bottom with parchment paper.
Remove cardamom seeds from their pods. Discard pods and crush seeds in a mortar and pestle. If you don’t have one, wrap the seeds in a newspaper and crush with a rolling pin (or the base of your frying pan). The seeds should not be crushed to a dust—the result should look like freshly cracked pepper. Set aside.
Melt chocolate and butter in a heatproof bowl set over a pan of simmering water, stirring gently. Take off the heat and add white and brown sugar, salt, espresso, and cardamom powder and stir to combine. Set aside and allow to completely cool.
Add eggs to chocolate mixture and stir to combine. Add flour and mix until smooth.
Pour the batter into the prepared pan and spread evenly. Bake for 25 to 30 minutes, or until a toothpick inserted in the middle comes out with moist crumbs. While baking, crush pistachios in a mortar and pestle (or use the same method you used to crush the cardamom).
When the brownies come out of the oven, garnish with pistachio dust, rose petals, and a shower of cocoa powder.
Cool in the pan on a rack, then use the parchment paper to lift out the brownies before slicing into squares.
Shayma Saadat is a cookery teacher, food writer, stylist and photographer who focuses on the food of her heritage - Pakistan, Afghanistan and Iran, which she refers to as Silk Route cuisine. Shayma lives in Toronto with her husband and son. You can follow her culinary journey on Instagram @SpiceSpoon.