Melt the white chocolate (if using) in a double boiler or microwave, stirring frequently to prevent burning, until smooth and drizzlable.

Drizzle the white chocolate randomly into the bottoms of your chocolate molds to create a marbled effect. Refrigerate to set.

Melt the dark (or milk) chocolate in a double boiler or microwave. Pour it into each mold, swirling to coat the sides completely. Pour out the excess chocolate back into the bowl and refrigerate the molds to harden.

Separate and cut the kataifi pastry into small pieces. Add it to a large dry skillet over medium heat and begin toasting.

Gradually pour in the melted butter while stirring to evenly coat the kataifi. Toast until it reaches a deep golden brown, stirring frequently to prevent burning.

Remove from heat and stir in the tahini until well combined.

Remove the chocolate-coated molds from the refrigerator. Fill each mold with the kataifi-tahini mixture, pressing gently to ensure an even layer.

Pour the remaining melted chocolate over the filling, spreading it evenly to seal the molds with a thin layer of chocolate.

Refrigerate the filled molds until the chocolate is fully set. Gently pop the chocolates out of the molds and serve.