450g (1lb) soft brown sugar
225g (8oz) black treacle
110g (4oz) unsalted butter
30ml (2 tablespoons) water
15ml (1 tablespoon) white vinegar
1 Line a 19cm (7½in) square shallow tin with non-stick baking parchment. Place all the ingredients into a large saucepan of at least 3 litre (5 pint) capacity. Bring to the boil very slowly over a low heat. This will take 10-15 minutes.
2 Once the sugar has dissolved completely, turn up the heat slightly and continue to boil until the temperature reaches 130°C/270°F on a sugar thermometer or soft-crack stage – this is when a small quantity of the mixture dropped into very cold water can be stretched between the fingers, separating into hard strands.
3 Immediately pour into the prepared tin and leave to set. Once set, turn the treacle toffee out and break into small pieces.