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. Melt chopped chocolate and butter together, stirring constantly until smooth and glossy. Remove from heat and cool slightly.
03 - Whisk egg yolks, granulated sugar, ground cardamom, and salt into the warm chocolate mixture until fully combined and glossy.
04 - In a chilled bowl, beat 1/2 cup cold heavy cream until soft peaks form. Set aside.
05 - In a separate clean bowl, beat egg whites until stiff glossy peaks form.
06 - Gently fold whipped cream into chocolate base until incorporated. Fold in beaten egg whites in two additions, being careful not to deflate the mixture.
07 - Divide half the chocolate mousse among 4 serving cups. Sprinkle with a layer of cooled pistachio crunch, then top with remaining mousse. Refrigerate at least 2 hours until set.
08 - Whip remaining 1/2 cup cold 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 extra chopped pistachios and dried rose petals.