If you're using frozen kataifi, thaw it according to the package directions and gently separate the strands.

Use kitchen scissors or a knife to cut the pastry into smaller pieces. This makes the finished filling easier to bite and slice. Melt the butter in a large skillet over medium heat. Add the kataifi and cook for about 6–8 minutes, stirring frequently. Keep cooking until the pastry is evenly golden brown and crisp.

Don't rush this step. Pale, undercooked kataifi can leave you with a soft filling instead of that delicious crunch. Once golden, transfer it to a bowl and let it cool for a few minutes.

Add the pistachio cream, tahini, and salt to the toasted kataifi. Stir gently until everything is evenly combined.

You want a mixture that's creamy but still has plenty of visible crispy pastry throughout. Don't mash the kataifi into a paste—the contrast between crunchy pastry and smooth pistachio is what makes these bars so good.

Place the chopped chocolate in a heatproof bowl. Melt it gently over a double boiler, stirring frequently. You can also use a microwave, heating it in short 15–20 second bursts and stirring thoroughly between each burst. Be careful not to overheat the chocolate.

For an especially glossy shell with a clean snap, you can temper the chocolate. However, tempering isn't essential for a homemade version. A simple melted chocolate shell will still taste fantastic.

Spoon some melted chocolate into a deep chocolate bar mold. Tilt the mold or use a pastry brush to spread the chocolate across the bottom and up the sides. Try to create a reasonably thick, even layer. Place the mold in the refrigerator for about 10 minutes, or until the chocolate is firm. If the sides look thin, add another layer of chocolate and chill again.

Once the chocolate shell has set, spoon the pistachio-kataifi mixture into each mold. Press it down gently so there aren't large air pockets, but don't pack it so tightly that you lose the fluffy crunch. Leave a little room at the top for the final chocolate layer.

Pour the remaining melted chocolate over the filling. Spread it carefully toward the edges so the filling is completely enclosed. Pay special attention to the corners and edges—this is what keeps the bars together when you unmold them.

Give the mold a gentle tap on the counter to release any trapped air bubbles.

Refrigerate the bars for 45–60 minutes, or until completely firm. Once set, carefully remove them from the mold. If you're using a silicone mold, gently pull the sides away from the chocolate before popping each bar out.

For a pretty finish, drizzle the bars with melted white chocolate and sprinkle them with chopped pistachios.