Also known as bonfire toffee or honeycomb. Or the inside of a Crunchie bar. Its wonderful bubbles are achieved by adding bicarbonate of soda to the toffee mix. There is a whole science lesson to be had in why and how that happens, so if you wanted to you could make preparing for Bonfire Night into a rather sticky chemistry lesson.
300g caster sugar (or some recipes use granulated)
200g golden syrup
2 tbsp white wine vinegar (or malt vinegar or cider vinegar)
2 heaped tsp bicarbonate of soda
20cm round or square cake tin
And the biggest pan you have. Really, the absolute biggest.
The method is very similar to treacle toffee so take a look at that for any extra detail.
1. Grease the tin, bring it near to the stove and have a jug or glass of cold water ready to hand for testing ‘hard crack’. (If you read about treacle toffee that sentence won’t seem quite so odd.) Make sure the bicarb is near to hand as you will need to get to it quickly. Put the sugar, syrup, vinegar and 150ml of water into the pan. Stir over a low heat to dissolve the sugar.
2. Once it has dissolved, whack the heat up high and stop stirring. Not stirring is important to the science. The mixture will boil and bubble and turn a lovely toffee colour. Let it go for ten minutes or so before starting to test for hard crack. Once you know that it is hot enough – either by your sugar thermometer or because a drop goes brittle in the glass of water – take it off the heat straight away. But do make sure that it at the right temperature or else your cinder toffee will sink.
3. Now as fast as possible stir in the bicarbonate of soda. And this is where it gets exciting. I really hope you aren’t making this on your own because you are going to want someone with you to witness the glorious spectacle. It will rise and rise and rise and rise. Just watch it, don’t stir. When it gets perilously close to the top of the pan, give it a stir and the volcano will subside.
4. Pour the toffee into the tin and leave to cool. You will already be able to see the glorious bubbles in it. When it is totally cold, tip it out of the tin and break it up. You may – like me – need to use the corner of a rolling pin.
The cinder toffee won’t stick together like treacle toffee, so you are fine just putting it into an airtight tin or a jar. It will keep for up to a week.