Melt 4 tablespoons of unsalted butter, over medium heat, in a large skillet. Add in the kataifi (8 ounces) and toast until deep golden brown and crunchy. Remove from heat and cool.
In a microwave-safe bowl, add the chopped chocolate bars. Microwave at 50% power for 3 minutes, stopping halfway to stir. Continue to heat at 30-second intervals until melted or near melted. Stir when done - the chocolate should be smooth and the consistency of thick syrup.
Place chocolate bar mold on a cookie sheet or flat pan. Pour a thin layer of the melted chocolate into the bar mold. Using a pastry brush, bring the chocolate up against the sides. Repeat. You'll want to make sure that the bottom and sides of each mold are fully covered. Gently shake then lift and drop your mold pan on the counter to get any bubbles out. Put the pan into the refrigerator on a flat surface and allow the chocolate to set for 10 minutes.
In a large bowl, fold the toasted kataifi, pistachio cream 91/2 cup), salt (1/2 teaspoon), and tahini (1/4 cup) until well incorporated.
Remove the chocolate mold from the refrigerator and place a thick layer of the pistachio mixture into each mold, filling them up to just below the top of the mold. Use a spoon to flatten the pistachio mixture down into it is even and flat. (You may end up with the extra pistachio mixture. Save for another use, of bake more bars).
Pour the remaining melted chocolate on top of the filling, then spread the chocolate to evenly coat. For a finished look, run a long, off-set spatula across each mold to remove any excess chocolate and create a nice even surface. Place the mold back into the refrigerator for at least 30 minutes.
Remove the chocolate bars from the molds. The bars will look so shiny and pretty from the design you make with the colored white chocolate! No two bars will be exactly alike. Trim any excess chocolate on the sides of the bar with a pairing knife. Keep refrigerated. Enjoy! Anywhere you bring these, you will be the Rock Star of the event! Promise!