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 let cool completely.
02 - Set a heatproof bowl over a pan of simmering water to create a double boiler. Add chopped chocolate and butter, stirring continuously until completely melted and smooth. Remove from heat and allow to cool slightly.
03 - Whisk egg yolks, granulated sugar, ground cardamom, and salt into the warm chocolate mixture until the texture becomes glossy and well incorporated.
04 - In a chilled bowl, whip 1/2 cup cold heavy cream using a hand or stand mixer until soft peaks form.
05 - In a separate clean bowl, beat egg whites with mixer until stiff, glossy peaks form.
06 - Gently fold whipped cream into the chocolate mixture using a spatula. Then fold in beaten egg whites in two separate additions, folding just until combined and no white streaks remain.
07 - Distribute half the chocolate mousse evenly among 4 serving cups. Sprinkle a layer of cooled pistachio crunch over the mousse, then top with remaining mousse. Refrigerate for at least 2 hours to set.
08 - Whip together remaining 1/2 cup cold heavy cream, powdered sugar, and rosewater until soft peaks form.
09 - Top each chilled chocolate cup with a generous dollop of rosewater cream. Sprinkle with additional chopped pistachios and dried rose petals if desired. Serve immediately.