1. In a large heavy based saucepan mix together the golden syrup, water and caster sugar. Use a pastry brush dipped in water to clean the sides of the pan or the sugar will burn.
2. Give it a really good mix before turning on the heat and bringing to the boil.
3. Once boiling pour in the whipping cream and stir in the unsalted butter.
4. Bring to the boil before reducing the heat to low-medium. Pop in a sugar thermometer.
5. Let the caramel get to 121°C (firm ball stage). Try not to go over or under, and please be patient as it will take at least 20 minutes.
6. In the meantime line a 30 cm x 25cm x 5cm greased brownie tin with parchment paper.
7. Once the caramel is exactly at the right temperature, turn off the heat and carefully pour it into the prepared tin.
8. Wait a minute or so before generously sprinkling over the green cardamom and the chopped hazelnuts.
9. Now you have to wait for the caramel to set, around 5 hours or overnight, before cutting into large chunks.