Melt the butter in a pan and add the kadaif and powdered sugar. Cook, stirring constantly, until the kadaif turns golden brown. Remove from heat and let cool. Mix with pistachio paste.

Melt the chocolate and pour it into a silicone mold. Use a brush to spread the chocolate on the base and sides, then refrigerate for a few minutes until the chocolate hardens.

Fill the cavities with the kadaif mixture and cover with the remaining melted chocolate. Refrigerate until set. Drizzle with chocolate sauce using a piping bag and sprinkle crushed pistachios.