Begin by finely chopping the kataifi pastry into small pieces, about 1 inch long. Gently fluff it with your hands to separate the delicate threads.
Melt the butter in a pot over medium heat, then add the chopped kataifi. Toast, stirring continuously, until it becomes beautifully golden brown and delightfully crispy. Use two forks to further separate strands for extra crunch. Let it cool completely.
In a heatproof bowl, melt the white chocolate. If using, stir in the vegetable oil for a smoother texture. Add the natural pistachio butter and a pinch of salt, mixing until fully combined. Allow this mixture to cool down completely.
Once cooled, gently fold the toasted kataifi into the pistachio cream until everything is evenly combined. If the mixture feels a bit soft, pop it in the refrigerator until it firms up.
Form 16 small balls, approximately 1.1 ounces each, from the pistachio-kataifi mixture. Place them on a tray lined with parchment or wax paper and freeze them until they are firm.
Using two forks, dip each frozen ball into the melted dark chocolate, ensuring it's completely coated. Shake off any extra chocolate, then place them back on the wax paper. Sprinkle with chopped pistachios for decoration. Let them set fully before serving.