Step 1: Finely chop the kataifi pastry into small bits. In a skillet over medium heat, melt the butter and add the kataifi. Stir constantly for 5-8 minutes until it is a deep golden brown and very crunchy. Remove from heat and let it cool in a separate bowl.
Step 2: Once the kataifi is cool, add the pistachio cream, tahini, and a pinch of salt. Stir until the pastry is completely coated and the mixture is thick. Set aside.
Step 3: Melt the dark and milk chocolate together using a double boiler or in 30-second increments in the microwave. Stir until completely smooth.
Step 4: Pour a thin layer of chocolate into your chocolate bar molds. Use a small brush or spoon to push the chocolate up the sides of the mold to create a shell. Place the mold in the freezer for 5 minutes to set.
Step 5: Remove the mold from the freezer and evenly distribute the pistachio kataifi filling among the bars, pressing it down gently. Leave a little space at the top for the final chocolate layer.
Step 6: Pour the remaining melted chocolate over the filling, smoothing it out with a spatula to seal the bars completely.
Step 7: Place the molds back in the refrigerator for at least 30-60 minutes, or until the chocolate is completely firm and snaps easily when removed from the mold.