Line a 9-inch square baking pan with parchment paper, leaving a 2-inch overhang on all sides. Working in 2 batches, process pistachios in a food processor until a very fine powder forms, about 40 seconds. Transfer to a medium bowl.

Combine sugar and 1/3 cup water in a medium saucepan over medium, stirring constantly to dissolve sugar. Continue cooking, undisturbed, until syrup reaches one-string consistency, about 230°F on a candy thermometer, 4 to 5 minutes.

Add pistachio powder, cardamom, and salt to sugar syrup. Reduce heat to low, and cook, stirring constantly, until mixture thickens and resembles wet sand, about 2 minutes. Transfer pistachio mixture to prepared pan; roughly press mixture into pan using a moistened rubber spatula. Lightly grease a small offset spatula with ghee, and press mixture into a flat, even layer. Let stand 15 minutes.

Place white chocolate in a small microwavable bowl. Microwave chocolate on medium (50% power) in 10-second intervals, stirring thoroughly between intervals, until melted and smooth, 2 to 3 minutes total. Pour melted chocolate over pistachio mixture in pan, and gently tilt to cover in an even layer of chocolate. Tap pan a few times on counter to level chocolate. Top with flowers and rose petals. Gently tap pan 2 times on counter to settle toppings. Freeze until set, about 20 minutes. Decorate with additional flowers and gold leaf, if desired. Using parchment as handles, transfer bark to a cutting board; remove parchment. Using a sharp chefs knife, cut bark into angular, bite-size pieces.