Gently melt the white chocolate chips in a microwave-safe bowl, heating in 30-second intervals and stirring until smooth. Drizzle this melted white chocolate into two 16-ounce chocolate bar molds. Place them in the freezer for about 10 minutes to set.
Next, melt 10 ounces of the milk chocolate chips using the same microwave method, stirring until mostly smooth. Fold in the remaining 2 ounces of milk chocolate chips and stir to combine. Pour about half of this chocolate over the set white chocolate in the molds, using a pastry brush to ensure it evenly covers the bottom and sides. Let it sit at room temperature for 5 minutes, then transfer to the freezer for 20 minutes to firm up.
While the chocolate layers are setting, melt the unsalted butter in a large skillet over medium-high heat. Add the finely chopped kataifi dough and cook, stirring continuously for approximately 10 minutes, until it turns beautifully golden brown and crispy.
Remove the skillet from the heat. Stir in the creamy pistachio butter and tahini until the kataifi is thoroughly coated. Allow this flavorful filling to cool in the pan for about 10 minutes.
Retrieve your chocolate molds from the freezer. Evenly divide the cooled pistachio kataifi mixture into the molds, spreading it out gently to fill them.
Pour the remaining melted milk chocolate over the pistachio filling, using an offset spatula to spread it smoothly and create a flat, even top.
Return the molds to the freezer for a final 20 minutes, or until the chocolate bars are completely set.
Once firm, carefully remove the bars from their molds. Slice into your desired pieces and enjoy this delightful, crunchy treat!