01 - Heat a small skillet over medium heat. Add pistachios and toast for 2–3 minutes until fragrant. Pour in honey, stir constantly to coat evenly, and continue cooking for 1 additional minute. Spread mixture onto parchment paper in a thin layer and allow to cool completely.
02 - Set a heatproof bowl over a saucepan of simmering water, ensuring the bowl does not touch the water. Add chopped chocolate and butter. Stir frequently until completely melted and smooth. Remove from heat and let cool for 5 minutes.
03 - Whisk egg yolks, granulated sugar, cardamom, and salt into the cooled chocolate mixture. Continue whisking until the mixture becomes glossy and thickened, approximately 2 minutes.
04 - In a chilled bowl, beat 1/2 cup cold heavy cream using a hand mixer or stand mixer until soft peaks form. Lift the beaters—peaks should droop slightly but hold their shape.
05 - In a separate clean bowl, beat egg whites until stiff glossy peaks form. Peaks should stand straight when beaters are lifted.
06 - Gently fold one-third of the whipped cream into the chocolate mixture to lighten. Add remaining cream and fold until just incorporated. Repeat with egg whites, adding in two batches and folding carefully to maintain airiness.
07 - Spoon half the chocolate mousse evenly among 4 serving cups. Tap cups lightly on counter to release air pockets. Sprinkle a layer of cooled pistachio crunch over mousse. Top with remaining mousse, dividing evenly. Refrigerate for at least 2 hours until set.
08 - Combine 1/2 cup cold heavy cream, powdered sugar, and rosewater in a chilled bowl. Whip until soft peaks form. Cover and refrigerate until ready to serve.
09 - Remove cups from refrigerator. Top each with a generous dollop of rosewater cream. Sprinkle with additional chopped pistachios and dried rose petals. Serve immediately.