01 - In a small skillet over medium heat, toast pistachios for 2–3 minutes. Add honey, stir to coat, and cook 1 minute more. Spread on parchment paper to cool.
02 - Melt chocolate and butter together in a heatproof bowl set over a pan of simmering water, stirring until smooth. Remove from heat and let cool slightly.
03 - Whisk egg yolks, sugar, cardamom, and salt into the chocolate mixture until glossy and well incorporated.
04 - In a separate bowl, whip heavy cream to soft peaks using a hand or stand mixer.
05 - In another clean bowl, beat egg whites to stiff peaks.
06 - Gently fold whipped cream into the chocolate mixture. Then fold in the egg whites in two additions until just combined, being careful not to deflate the mixture.
07 - Divide half the chocolate mousse among 4 serving cups. Sprinkle a layer of pistachio crunch, then top with remaining mousse. Refrigerate at least 2 hours until set.
08 - Whip heavy cream, powdered sugar, and rosewater to soft peaks just before serving.
09 - Top each chocolate cup with a generous spoonful of rosewater cream. Garnish with extra pistachios and dried rose petals if desired.