01 - Toast pistachios in a small skillet over medium heat for 2–3 minutes. Add honey, stir to coat evenly, and cook for 1 additional minute. Spread mixture on parchment paper and allow to cool completely.
02 - Combine chocolate and butter in a heatproof bowl set over a pan of simmering water (bain-marie). Stir continuously until completely smooth and melted. Remove from heat and let cool slightly.
03 - Whisk egg yolks, granulated sugar, cardamom, and salt into the warm chocolate mixture until combined and glossy.
04 - In a chilled bowl, whip cold heavy cream until soft peaks form.
05 - In a separate clean bowl, beat egg whites until stiff peaks form.
06 - Gently fold whipped cream into the chocolate mixture until just incorporated. Fold in beaten egg whites in two separate additions, taking care not to deflate the mixture.
07 - Distribute half the chocolate mousse equally among 4 serving cups. Add a layer of cooled pistachio crunch, then top with remaining mousse. Refrigerate for at least 2 hours until set.
08 - Whip heavy cream with powdered sugar and rosewater until soft peaks form.
09 - Top each chilled chocolate cup with a generous dollop of rosewater cream. Garnish with additional chopped pistachios and dried rose petals if desired. Serve immediately.