Makes about 20 pieces
Line a 8in. square baking pan with lightly oiled foil. Half fill the sink with cold water and have ready a whisk and the bicarbonate of soda.
Place the sugar, syrup, cream of tartar, and vinegar into a medium-size, solid-based saucepan. Add 5 tablespoons water and set the saucepan over medium heat. Stir until the sugar has dissolved, then bring the mixture to a boil. Continue to cook until the mixture turns amber-coloured and reaches 'hard crack' stage, or 300°F (154°C) on a sugar thermometer.
As soon as the caramel reaches the right temperature, remove the saucepan from the heat and plunge into the sink of cold water to speed up the cooling process. Working quickly, pour the bicarbonate of soda into the caramel and whisk to combine evenly; the mixture will foam up quite a bit. Pour into the prepared baking tin in an even layer and let cool.
Melt the chocolate in a bowl set over a saucepan of barely simmering water or in the microwave and stir until smooth. (Click this link for tips on how to melt chocolate correctly). Remove from the heat and cool slightly. Turn the honeycomb out of the pan, peel off the foil, and break into chunks.
Half dip each piece into the melted chocolate. Let harden before packaging.
Stored in an airtight container, it will keep for 2-3 days.