Line a steel tray with silicone or greaseproof paper. Place aside until needed.
Put all ingredients except the bicarbonate of soda in a pot. Over medium heat, bring to a boil and cook for about 7 minutes.
Once it's a golden color and about 154°C/309˚F, remove the pot and place it somewhere safe for a minute for the bubbles to subdue.
After a minute, add the bicarbonate of soda to the caramel with a spoon and stir quickly. Don't use a whisk! It will foam up and start to expand.
When it does this, quickly pour it onto the tray lined with the silicone paper.
Be very careful, as the caramel is extremely hot. Allow it to cool thoroughly, break it into small shards, and store it in an airtight container.