Preheat the oven to 180℃, line a baking tray with baking paper, and slice the croissants in half. Set aside.

To make the pistachio frangipani, add the butter to a mixing bowl and beat until pale. Add the castor sugar and beat again. Add the egg and beat until combined. Add the pistachio powder, corn flour, salt, and whisk until smooth. Set aside.

To make the kunafa filling, cut the kunafa pastry into small pieces and toast in a large sauté pan on low to medium heat, stirring constantly, until golden brown and crunchy. Transfer to a mixing bowl and add the pistachio paste and tahini. Gently stir to combine.

Fill each croissant with 3 tbsp of the frangipani filling and top with 2 tbsp of the kunafa filling. Close the croissants and top them with 1 tbsp of the frangipani filling. Bake for 15-18 minutes until golden and cooked.

To make the pistachio buttercream, blend the remaining butter, pistachio butter, icing sugar, and almond extract until smooth. Transfer to a piping bag and refrigerate.

Melt the milk and dark chocolate in a bowl in the microwave at 10-second intervals, stirring between each until smooth. Toast and chop the pistachios.

After baking, if the frangipani has oozed out, trim excess for a cleaner look. Cover the croissants with melted chocolate or half-cover them. Pipe the pistachio buttercream and top with the remaining kunafa filling. Finish with pistachios and sea salt flakes.