After some thought, I realised that butter was probably the culprit, as anyone who cooks will tell you that butter will burn at higher temperatures. Also, I know honey doesn't like high heat and I wasn't sure if golden syrup was burning too. I do know that glucose syrup is stable at high temperatures (food science lessons came in handy there!), so decided to give that a try and hey presto! It worked. This has been tripled tested, and I guarantee it will work - it's so quick to make, and delicious coated in Cadbury Dairy Milk chocolate, just like a Crunchie bar!
Make sure you make this in a large saucepan as the bicarbonate of soda will puff up the hot mixture considerably - and quickly! It will also change colour as it rises in the pan - children might like to watch this being made, but due to the crazy temperature of the sugar syrup, they should stand well back!
140g glucose syrup (it's easier to cut the other end off the tube if you get the stuff in the 140g squeezy tubes!)
400g (2 cups) caster sugar
120ml (1/2 cup) water
2 tsp bicarbonate of soda, sifted (sounds silly to sift such a small amount, but you want NO lumps)
Line a 22cm square pan (or equivalent rectangular pan) with baking paper, or alternatively use a silicone one on a baking sheet with no need to line (these work great for this recipe!).
Put the syrup, sugar and water into a large saucepan and stir over a medium heat until the sugar dissolves.
Increase the heat and bring to a boil, without stirring. It will change from cloudy to clear around 100C. If you have a sugar thermometer, you need to reach the hard crack stage, or 148C. If you don't have a sugar thermometer it really doesn't matter - just carefully take a small amount and drop into a glass of cold water. If it has reached hard crack stage it will form brittle strands or clumps that will snap or crumble when it cools - if they just bend or squish, then you need to keep raising the temperature, you may find you need to put your hob on full heat. The sugar syrup will start to go a very light straw colour.
Immediately remove from the heat and add the bicarbonate of soda, whisking it in quickly. Allow it to puff up (it will deepen in colour after a few moments) then immediately pour into the tin and leave until completely cold and set, about 2 hours.
Snap or chop the cinder toffee into shards and serve as is, or coat in melted chocolate. You could also smash some up and enjoy as a delicious ice cream topping. Store in an airtight container for a few days (high humidity will cause it to become sticky, but still delicious!). Makes a sweet gift, or a lovely traditional treat on Bonfire Night (5th November in the UK).
See more images from this shoot at Stock Food.