Make the bars: Heat oven to 350 degrees. Line a 9-inch square baking pan with parchment paper such that the paper spills out over the sides of the pan, like wings.

In a food processor, pulse the pistachios until the nuts are very finely ground. Don’t let them get pasty. Add the flour, salt, baking powder and cardamom and pulse to combine.

In a large mixing bowl, whisk together melted butter and brown sugar until smooth and shiny. (The butter will separate at first, then blend in.) Whisk in the eggs until incorporated. Add the pistachio mixture and mix with a silicone spatula to combine. Gently stir in the white chocolate chips until evenly distributed. Pour the batter into the prepared pan and spread in an even layer.

Bake until the sides are brown and pull away from the pan, and the middle is slightly paler in color, 25 to 27 minutes. A toothpick inserted in the centre will come out with a few crumbs attached. Cool completely in the pan on a rack.

While the bars cool, make the frosting: Finely grind the saffron threads in a mortar using a pestle or in a microwave-safe bowl using the back of a spoon. If needed, transfer the ground saffron to a microwave-safe bowl or to a small saucepan if you don’t have a microwave. Stir in the milk, and microwave on high or heat over medium until the mixture is frothing around the edges but not boiling, about 30 seconds. Place the bowl in the refrigerator or freezer to quickly cool the mixture.

Meanwhile, in a large bowl, use an electric hand or stand mixer or a heavy whisk or wooden spoon to beat the cream cheese and butter until smooth. If working by hand, this takes some muscle. Add the confectioners’ sugar and salt and beat again until homogeneous and no clumps of sugar remain. Beat in the cooled saffron milk until well-combined. The frosting will turn a bright golden hue.

Once the bars have cooled completely, scrape the frosting over the top, and use a spatula to spread it evenly. Crush or chop some pistachios for garnish and sprinkle all over the top. Refrigerate for at least 2 hours before eating. The bars keep in an airtight container in the refrigerator for up to 5 days or in the freezer for 1 month.