If you're adding a visual flair, first melt the 2 tablespoons of white chocolate chips. Drizzle small amounts artfully into the pockets of your chocolate molds. Set these aside to firm up slightly.
In a small, microwave-safe bowl, combine the 2 cups of dark chocolate chips with 1 tablespoon of the coconut oil. Gently microwave in 20-second intervals, stirring thoroughly after each, until the chocolate is smooth and fully melted.
Spoon about 2 tablespoons of the melted dark chocolate into each mold. Use a spoon or a clean silicone brush to spread the chocolate evenly over the bottom and up the sides of the molds. Place the molds in the fridge to set while you get the filling ready.
On a cutting board, finely chop the 6 ounces of kataifi pastry dough. The finer the chop, the better it will mix and provide that signature crunch.
Heat the remaining 2 tablespoons of coconut oil (or butter) in a pan over medium heat. Add the chopped kataifi to the pan. Cook for a few minutes, stirring continuously, until it turns a lovely golden brown and becomes wonderfully crispy. Keep an eye on it to prevent burning!
Remove the pan from the heat. Stir in the 8 ounces of raw pistachio butter and the 1 tablespoon of tahini (if you're using it for extra depth). Mix everything together well until you have a uniform, crunchy pistachio filling.
Retrieve your set chocolate molds from the fridge. Divide the pistachio filling mixture equally among them, spreading it out evenly over the firm chocolate base.
Spoon another 2 tablespoons (or more, if needed) of the remaining melted dark chocolate over the pistachio filling in each mold. Gently spread it out with a spoon or brush to completely cover the filling.
Place the filled molds back into the fridge for about 20 minutes, or into the freezer for 10 minutes, until they are completely firm. Carefully pop the chocolate bars out of their molds. Remember, these bars are quite rich, so cutting them in half makes for a perfectly healthy single serving!