01 - In a small skillet over medium heat, toast pistachios for 2–3 minutes. Add honey, stir to coat evenly, and cook 1 minute more until caramelized. Spread mixture on parchment paper to cool completely.
02 - Set a heatproof bowl over a pan of simmering water to create a bain-marie. Melt chocolate and butter together, stirring continuously until smooth and glossy. Remove from heat and let cool slightly.
03 - Whisk egg yolks, sugar, cardamom, and salt into the warm chocolate mixture until fully incorporated and the mixture appears glossy and thickened.
04 - In a chilled bowl, whip cold heavy cream using a hand or stand mixer until soft peaks form. Do not overbeat.
05 - In a separate clean bowl, beat egg whites with a mixer until stiff glossy peaks form.
06 - Gently fold one-third of the whipped cream into the chocolate mixture to lighten it. Fold in remaining cream, then gradually incorporate the egg whites in two additions, folding just until no white streaks remain. Be careful not to deflate the mixture.
07 - Divide half the chocolate mousse evenly among 4 serving cups. Sprinkle an even layer of cooled pistachio crunch over the mousse. Top with remaining mousse, smoothing the surface. Refrigerate for at least 2 hours until set.
08 - Whip heavy cream, powdered sugar, and rosewater together in a chilled bowl until soft peaks form. The cream should hold its shape but remain light and airy.
09 - Top each chilled chocolate cup with a generous dollop of rosewater cream. Garnish with extra chopped pistachios and dried rose petals if desired. Serve immediately.