Cinder toffee

Line a 15cm square tin with greaseproof or parchment paper.

Put the syrup, sugar, butter and water into a large heavy-bottomed pan set over a medium heat. Stir until the sugar has dissolved, before turning up the heat and bringing to the boil.

Cook, without stirring until a teaspoon of the hot toffee mixture becomes a hard ball when dropped into a jug of cold water. If you have a sugar thermometer, it should register 138C. Remove the pan from the heat.

Add the vinegar and bicarbonate of soda to the pan - take care as the toffee mixture will bubble up and rise in the pan. Pour immediately into the lined tin and leave on one side.

After about 15- 20 minutes, when the mixture has begun to set, score the toffee in square shapes, using a sharp knife. Break along the lines when it has completely set. The toffee will keep in an airtight tin for up to two weeks.