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 allow to cool completely.
02 - Set a heatproof bowl over a pan of simmering water to create a bain-marie. Add chopped dark chocolate and unsalted butter, stirring constantly until completely melted and smooth. Remove from heat and let cool slightly.
03 - Whisk egg yolks, granulated sugar, ground cardamom, and salt into the cooled chocolate mixture. Continue whisking until the mixture becomes glossy and well incorporated.
04 - In a clean mixing bowl, whip 1/2 cup cold heavy cream using a hand or stand mixer until soft peaks form.
05 - In a separate bowl, beat egg whites with clean beaters until stiff peaks form.
06 - Gently fold the whipped cream into the chocolate mixture until just combined. Then fold in the beaten egg whites in two separate additions, being careful not to deflate the mixture.
07 - Divide half of the chocolate mousse evenly among 4 serving cups. Sprinkle a layer of cooled pistachio crunch over the mousse, then top with the remaining mousse. Refrigerate for at least 2 hours to set.
08 - Whip together 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. Garnish with additional chopped pistachios and dried rose petals if desired. Serve immediately.