01 - Toast pistachios in a small skillet over medium heat for 2-3 minutes. Add honey, stir to coat evenly, and cook 1 minute more. Spread mixture on parchment paper to cool completely.
02 - Set a heatproof bowl over a pan of simmering water. Add chocolate and butter, stirring constantly until melted and smooth. Remove from heat and let cool slightly.
03 - Whisk egg yolks, sugar, cardamom, and salt into the warm chocolate mixture until glossy and fully incorporated.
04 - In a chilled bowl, whip cold heavy cream to soft peaks using a hand or stand mixer.
05 - In a separate clean bowl, beat egg whites to stiff peaks.
06 - Gently fold whipped cream into the chocolate base until just combined. Then fold in egg whites in two additions, being careful not to deflate the mixture.
07 - Divide half the mousse 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 to soft peaks just before serving.
09 - Top each chilled chocolate cup with rosewater cream. Sprinkle with extra pistachios and dried rose petals if desired. Serve immediately.