Preheat the oven to 180°C/350°F.

Prepare the sugar syrup: add the granulated sugar and water to a small saucepan. Add the split cardamom pods and rosewater, if using. Stir with a spoon and cook over low-medium heat until the sugar is just dissolved. Set aside for later use.

Add the pistachios to a blender or food processor and blitz into a powder, taking care not to overblend as the pistachios will start to release oils.

In a medium bowl, cream together the butter and powdered sugar. Add the egg, salt, and ground pistachios and mix until combined.

Slice each croissant in half lengthwise. Use a pastry brush to generously brush the interior side of each croissant slice with the sugar syrup.

Pipe or spread the pistachio filling onto the bottom half of each croissant, ensuring you evenly cover the croissant.

Add the top layer to each bottom-half and brush the top with more sugar syrup. Side note: Any leftover syrup can be used in iced coffee!

Pipe a little more filling on top of each croissant and sprinkle with slivered pistachios.

Transfer the croissants to a baking tray and bake for 12-15 minutes until golden. Keep an eye on them at the 12 minute mark as they may burn.

Leave the croissants to cool slightly before dusting with powdered sugar and enjoying with your favourite beverage.