Preheat your oven to 180°C (350°F) and line a large tray with baking paper.

In a pot, add the sugar and water, stir, and place on medium heat until it comes to a boil. Lower the heat and simmer for about 2 minutes, then let it cool.

Process the pistachios in a food processor until they become fine crumbs.

In a large bowl, beat the softened butter, icing sugar, and vanilla together for 5 minutes.

Add the egg and mix well. Incorporate the ground pistachios, corn flour, salt, and milk until you have a thick, spreadable mixture.

Cut the croissants in half horizontally. Brush syrup onto the cut sides.

Pipe or spread the filling onto the bottom half of the croissants and place the top half back on.

Spread a little filling on top and press chopped pistachios onto it.

Bake for around 20 minutes until golden brown and crispy. Let cool slightly, then dust with icing sugar and serve.