Bring all the ingredients except the vinegar to the boil stirring constantly

Boil gently for 15-20 minutes, still stirring, until the mixture becomes brittle when a small piece is dropped into cold water. Even better, if you have a jam thermometer the temperature needs to reach the hard crack stage of 149-154°C / 300-310°F

Stir in the vinegar and then pour into a well-greased tin

When nearly set, you can score it deeply into squares. Alternatively, allow to cool and give it a bash with a toffee hammer

Store in an airtight jar or container